I always just use version or date, and then break it into sections just incase I want to go back to something.

So say I am working on a new alien, I will start with:

AlienBlocking (for blocking out a body)
AlienBlockingV2 or AlienBlocking092206
AlienBlockingV3 or AlienBlocking092306
etc.

AlienDetails (for after blocking and doing muscle structure)
AlienDetailsV2 or AlienBlocking092406
etc.

AlienShaded (for UV shading after details are complete)
AlienShadedV2 or AlienShaded092506
etc.

AlienPose (for after rigging and shading is done)
*follow above format*

AlienFinalRender (for after posing and in an environment)
*follow above format*

Hope that helps.