in the USA we have this stuff called "Goo Gone" it's a natural product that smells like oranges...
I always keep a couple of bottles. I've used it on TONS of CEs and it's never leaves any damage and always gets 100% of the sticky stuff off... it's even strong enough to remove bits of tar from the body of your car.
On used games GameStop loves to put their barcode stickers under the cover plastic (as in right on the paper artwork that makes up the cover, spine and back)... Goo Gone is even delicate enough to use right on the paper, you have to be careful because some of it will absorb but it really does work.