I have used GooGone to remove the type of stickers with paper layer on top of the adhesive layer. For those, it works really, really well. Just soak the sticker directly with the GooGone and wait a few minutes. The sticker should just lift off.

Back in college I worked at the campus bookstore and when we stickered the price of the textbook on the cover. At the end of the quarter any unsold books had to be returned and we usually spent a good part of a week removing stickers. Any damage to the book meant we couldn't return it so the GooGone was really nice as it completely removed any sticky reside without any damage.

The lemon smell of the stuff is nice at first, but by day two the smell horrible, but as a collage student I was just happy to have a job!!