There are two things I use a lot for removing stickers/decals/pricetags.
1. Goo Gone
This is strong stuff, good for most things. It does have some drawbacks. It shouldn't be used on clear plastic, most of the time it will ruin it. Because it is strong it can sometimes discolor dyed plastic. It has a stupid strong citrus smell, you better like oranges if you use this product...
2. WD-40
I was surprised to learn that this stuff removes adhesive, also it doesn't ruin most clear plastics. The only problem, it's a little harder to work with and I know some petroleum products break down rubber. It also is a little more involved to clean up. I use this a lot of time on CD/DVD cases to remove little bits of price tags.
Always read the bottle warnings and test on a small spot of the surface you want to clean before really going at it. There are no 100% safe guarantees when using any of these types of products.
Also I have used Goof Off, but that is way to strong. I stopped and substituted for the two solutions I just mentioned... It is really good, but so smelly and industrial grade. Once you smell it, it makes you want to play Dark side of the Moon, eat a bunch of munchies and take a nap.
-baker