Here is a method that can be dangerous, but often works quite well for me.
Naptha, old-fashioned cigarette lighter fluid (like the yellow plastic bottles by Ronsonol) is great for dissolving the type of adhesives found under stickers, but it can be damaging to plastics. Test first!
If the label is in an indentation, I put in a couple of drops and let it swim and seep in around the edges for 10-20 seconds. This should loosen the adhesive, at least at the edge, and I start prying it up with a sharp blade such as an Xacto knife. Sometimes I add a few more drops. Don't let it run away and get onto something important such as a circuit board!
After the sticker is up, use a paper towel and more naptha to remove all traces of adhesive, then use soap and water or alcohol to remove all traces of naptha. Work quickly, if you can do the whole thing in a minute or two your chances of damaging the surrounding plastic are greatly reduced.
