Hmmm, I bought CameraBag and its a bit of a one-trick pony. It allows you to add some limited effects to you're images (as you see on the screen shots). But thats all - you can't really customise the effects.
My vote goes to Photogene - its like a mini photoshop on you're phone. It allows you to alter colour levels, crop, straighten, add a couple of effects. All you could want to do with images on you're phone really!
I use snapture too but too bad its only available for jailbroken phones.