I know that Aquila over on the Daz fourms is making a Space Marine outfit for The Freak using Anim8tor (Free).
Or you could use Wings3d (also free)
I personaly like Hexagon(bought from Daz), even with it's bugs and other problems.
Then There's Silo (bought from Nevercenter). No comment on this one never used it although the interface looks VERY userfriendly.
Blender (again free) has a very steep learning curve, I'm near the starting line and hope to move up to being able to move the camera soon, lol.
Then there are the heavy hitters, that heavy on the wallet, 3d Studio Max, Lightwave and Carrara. 

I'll assume you don't have much or any skill in modeling since from what i've learned, makeing basic clothing is infinatly easrier than modeling a person or animal. Although others might disagree. My first bit of advice, which I'm sure others will also give is basicly try out everything, most pay products have free trails. Though I'd say try Wings3d and Animator first. They may be free but that dosen't mean that they aren't powerful. They are both good for beginners.

 If you need tutorials on how to make clothes then check out the Hexagon Forum over at Poserpros. I believe that the tutorials will transfer to other apps easily because box-modeling is box-modeling.

I hope this long winded reply is helpful in some way.