Using a hair dryer, heat up the offending sticker for a minute or so. Start peeling. Apply more heat as needed. It should come off without too much fuss.
It even works with stock stickers.
*Edit - this method also allows for you to re-use the sticker. So if you're giving it a paint job, you can reapply the stickers if you so choose.
If you do have residue, there's no need for expensive goo-be-gone products. Just your hair dryer and some cheap hand sanitizer.
Apply heat to residue and apply hand sanitizer. Allow a few seconds for the hand sanitizer to react with the residue. Apply a little more and with a little finger muscle, simply rub it off.
Edited by makeitgo, 20 May 2013 - 07:39 PM.