You've got a very dark gray in your palette but you've used it so scarsely. The places that the cap is supposed to drop shadow could use some of that dark gray as dithering. Also the inner corners need not be light gray.

I share XQbit's sentiments.  That being said, you already have the right colors, it's just a matter of application.  Don't be afraid to shrink your highlights and wrap those shadowy colors right around them.

Has to be darker, this one's just to bright. Otherwise, nice. 

Preview is dowsized and considered NPA. all you have to do is crop part of the actual image sot it's 100x100 or less, you'l probably wanna crop it to 64x64 so u can still use it as an avy :)

also should have a boarder or transparent Background instead of just white.

BTW I really like it, noice darth vader