Let's face it, at the moment the Sisters of Battle are the least effective race in 40k- which is hardly surprising since they were originally designed as more of a force for special scenarios, or as an ally contingent. In the new 40k, where allies are pretty rare, they need some help to become a truly stand-alone force.

The Problems

1)Range
As it stands, the Sisters are out-ranged by every other race in 40k. Even Tyranids can shoot farther, and generally more effectively. On its own, this isn't a problem- the Sisters are supposed to be a short-ranged force- but it leads nicely into the second problem...

2)Mobility
The Sisters just don't have the speed to get their short-ranged weapons into position. Immolators and Rhinos are standard speed APCs, and Seraphim squads are equipped with few weapons which can take out tough targets- only melta-bombs can do it, and this will leave the Seraphim so exposed as to sign their death warrant (after all, there's no reason for the tank to stay off open ground). Coupled with the short range of their weapons, this makes it very hard for the Sisters to take out hard targets.

3)Skill
The Sisters are overall the least skillful troops in 40k. In their entire army list, a grand total of one unit gets a WS or BS or 4- and that's the Canoness! Even Imperial Guard have access to better Elites and as skillful commanders. If you finally do manage to get a Multi-Melta into position to fire, it takes nerves of steel to trust your one chance to kill a tank to someone with a BS of 3.

Extreme Example:
Consider Sisters of Battle vs. Chaos Space Marines. Included in the Chaos army are a Land Raider, Chaos Dreadnought with twin autocannon, and some Raptors. The Land Raider is invulnerable to every weapon in the opposing army except the Melta weapons, and even these need to get very close indeed to have any chance of damaging it. The Dreadnought can gun down Sisters at will so long as it avoids getting within 24" of a Multi-Melta- they have no way to hit back. Any Rhinos or Immolators trying to deploy squads in range are easy meat to lascannon and autocannon fire, even without taking the rest of the Chaos army into account. Every weapon in the Chaos force will be pointed at the unfortunate Seraphim- the only troops who can kill tanks if they take Melta-bombs. Finally, the Raptors can outmanoeuvre and outfight everything in the Sisters force- only Seraphim can catch them, and they lack both the skill and the weapons to do any appreciable damage. The concept of the Sisters trying to stop Daemon Princes or Greater Deamons doesn't bear thinking about...

Solutions

1)The 'Space Marines in Lipstick' solution
One approach is simply to use the Sisters of Battle models as Space Marines. Even without converting troops into types for which the Sisters have no equivalent, like Bikers, the extra heavy weapons and vehicles make up for the problems nicely. Of course, this is only an option if the only reason you play Sisters of Battle is the figures.

2)Jigger with the list a bit
Here are a few suggestions for additions and alterations to the army list which still preserve the feel of the army.

Upgraded BS.
The Sisters really, really need their BS of 4. This increases the cost for all choices by 2pts, including the Canoness (who becomes BS 5). I know the new 40k is supposed to level out stats a bit, but considering the multitude of special rules for most other races this hardly seems extreme or overcomplicated.

HQ

0-1 Canoness

Weapons: Bolt Pistol

Options: The Canoness may have up to two choices from the Sisters of Battle Weapons List. The Canoness may have a Jump Pack at +20pts, and twin-linked bolt pistols at +4pts. If she uses the Jump Pack option, her Celestians must also take jump packs (see Celestian Squad entry)

Bodyguard: The Canoness may be accompanied by 4 to 9 Celestians at +13 points per model.

Weapons: The Celestians are armed with bolt guns.

Options: Up to one Celestian may be armed with the following weapons: Heavy Bolter +10 points, Heavy Flamer +15 points, or a Multi-Melta at +25 points.

The whole squad may have Frag Grenades at +1 points per model, Krak grenades at +2 points per model and Melta-Bombs at +4 points/model.

Up to one Celestian may be armed with a flamer at +3 points or a meltagun at +10 points.

Jump Packs: The squad may have jump packs at +20 points/model. No models may have both a heavy weapon and a jump pack.

Characters: Up to one Celestian may be upgraded to a standard bearer at an additional cost of +10 points. Any Battle Sister unit with a model within 6" of the standard bearer may add +1 to their weapon skill.

Rhino: The squad may be mounted in a Rhino APC at a cost of 50 points unless they have jump packs.

Immolator: If the squad numbers 6 or fewer models, without jump packs, it may be mounted in an Immolator at an additional cost of +70 points.

ELITES

Celestian Squad

Squad: The squad consists of one Sister Superior and between 4 and 9 Celestians.

Weapons: The Celestians are armed with bolt guns. The Sister Superior may exchange her boltgun for a bolt pistol and close combat weapon at no extra points cost.

Options: Up to one Celestian may be armed with the following weapons: Heavy Bolter +10 points, Heavy Flamer +15 points, or a Multi-Melta at +25 points.

The whole squad may have Frag Grenades at +1 points per model, Krak grenades at +2 points per model and Melta-Bombs at +4 points/model.

Up to one Celestian may be armed with a flamer at +3 points or a meltagun at +10 points.

Characters: The Sister Superior may be upgraded to a Veteran Sister Superior at a cost of +10 points. The Veteran Sister Superior may also be given a single choice from the Sisters of Battle Weapons LIst.

Rhino: The squad may be mounted in a Rhino APC at a cost of 50 points.

TROOPS

Battle Sisters Squad

Squad: The squad consists of one Sister Superior and between 4 and 9 Battle Sisters.

Weapons: Boltguns. The Sister Superior may exchange her boltgun for a bolt pistol and close combat weapon at no additional points cost.

Options: Up to one Battle Sister may be armed with one of the following weapons: Heavy Bolter at +10 points, Heavy Flamer at +15 points, or a Multi-Melta at +25 points.

Up to one Battle Sister may be armed with a flamer at +3 points or a Meltagun at +10 points.

The squad may be armed with Frag Grenades at +1 points/model and Krak Grenades at +2 points/model.

Characters: The Sister Superior may be upgraded to a Veteran Sister Superior at a cost of +10 points. The Veteran Sister Superior may also be given a single choice from the Sisters of Battle Weapons LIst.

Rhino: The squad may be mounted in a Rhino APC at a cost of 50 points.

FAST ATTACK

Seraphim Squad

Squad: The squad consists of one Sister Superior and between 4 and 9 Seraphim.

Weapons: Twin-linked bolt pistols and frag grenades. The Sister Superior may exchange her bolt pistols for a bolt pistol and close combat weapon at no additional points cost.

Options: Up to one Seraphim may replace her bolt pistols with twin hand-flamers (count as a single flamer) for an additional cost of +6 points.

The squad may be armed with Krak Grenades at +2 points/model and Melta Bombs at +4 points/model.

Characters: The Sister Superior may be upgraded to a Veteran Sister Superior at a cost of +10 points. The Veteran Sister Superior may also be given a single choice from the Sisters of Battle Weapons List.

Jump Packs: The squad are equipped with jump packs.

Land Speeder

Limited Numbers: Battle Sister Land Speeders are fielded individually, not in squadrons.
Type: Fast,Skimmer (not open-topped due to power armour)
Crew: Battle Sisters
Weapons: Heavy Flamer.
Options: The Heavy Flamer can be upgraded to a Multi-Melta at +15pts.

Bike Squadron

Squad: Squad consists of 1 Sister Superior and 2-5 Battle Sisters riding bikes.
Weapons: Each bike has twin-linked bolters. Each biker is armed with a bolt pistol.
Options: Up to two Sisters may have: flamer at +3pts, Meltagun at +10pts.
Character: The Sister Superior may be upgraded to a Veteran Sister Superior at +10pts. The Veteran Sister Superior may be given a single choice from the Sisters of Battle Wargear List.

HEAVY SUPPORT

Retributor Squad

Squad: The squad consists of one Sister Superior and between 4 and 9 Battle Sisters.

Weapons: Boltguns. The Sister Superior may exchange her boltgun for a bolt pistol and close combat weapon at no additional points cost.

Options: Up to four Battle Sisters may be armed with one of the following weapons: Heavy Bolter at +10 points, Heavy Flamer at +15 points, or a Multi-Melta at +25 points.

The squad may be armed with Frag Grenades at +1 points/model and Krak Grenades at +2 points/model.

Character: The Sister Superior may be upgraded to a Veteran Sister Superior at a cost of +10 points. The Veteran Sister Superior may also be given a single choice from the Sisters of Battle Weapons List.

Rhino: The squad may be mounted in a Rhino APC at a cost of 50 points.

Immolator: If the squad numbers six or fewer models then the entire squad may be mounted in an Immolator at an additional cost of +70 points.

Immolator

Type: Tank

Crew: Battle Sisters

Weapons: Inferno Cannon (Template, Strength 6, AP 4, Heavy 1. Squads taking casualties must make a Fall Back move)

Razorback

Type: Tank

Crew: Battle Sisters
Weapons: Twin-Linked Heavy Bolters
Options: The heavy bolters may be upgraded to: Twin-linked Lascannon +20pts, Multi-Melta +5pts.
Transport: The Razorback may carry up to 6 Battle Sisters.

Comments on the additions.

Celestian Retinue Upgrades: This allows the Celestian Retinue to become elite Seraphim. The main reason for this is so they will at least have some chance of hitting simultaneously with most other troops. It also allows the creation of a jump-packing command squad (for those people who have made Seraphim command squads from the old codex, for example.) which fits the whole hard-and-fast, close quarters philosophy well.

Land Speeders: The addition of Land Speeders is deliberately very limited- only one per fast attack choice, and only the two classic Ecclesiarchy weapons- Flamer and Melta. As well as having Land Speeders made for them in small numbers, the Sisters could also use civilian skimmers with a Retributor leaning out of the window, so the idea of them having this very limited option makes some sense.

Bike Squads: Bikers also fit in well with the way the Sisters operate. They provide some extra mobility, and at least some chance of destroying armour with short-ranged meltagun fire. As with the Land Speeders, I've limited them to Flamer and Melta weapons to fit in with the rest of the force. Again, these could be seen as custom-built bikes, or commandeered civilian ones.

Razorbacks: It's important to note that the Razorback is a HEAVY SUPPORT CHOICE ONLY. It's intended to represent exactly what it is- a make-do stop-gap vehicle. Since the Razorback is essentially an Immolator with a different weapons fit, there is no reason why the Ecclesiarchy would not have them, but they would be rare. This is the only unit in the army list with access to Lascannons, giving the Sisters some sort of ranged anti-tank punch without turning them into a tank-nut army.

A note on models

Obviously some conversion would be necessary to use some of these suggestions. A Sisters of Battle Land Speeder is not too hard to do, just involving the replacing of the crew. Bikers are harder to do since more of the rider is visible. but can probably be made from Seraphim. A Sisters of Battle Razorback is very easy to make by combining the Razorback with the Immolator's decorated armour plates and gunner. All this would of course be much easier if we had some plastic Battle Sisters though.....

Conclusion

Well, there it is. I hope some of this will be useful to someone out there in GW land. I think I've made suggestions that make the army more solid without losing its character. Now, lets go find some heretics before my brand gets cold....