Personally, my tried-and-true method is to use a blow-dryer. Just aim the heat all over the label for about 5-10 mins. It will dry out the adhesive and the entire thing will come off in one clean piece. Test one little corner after a couple minutes before removing the entire thing. You will not believe how easy and smooth this is.
LifeHacker also suggests using peanut butter or a standard pink eraser to get rid of the leftover gunk. Sharon Cole, of A Dream Wedding, told me that Goo Gone is her best friend when it comes to removing extra gunk when you're on the go (which a wedding coordinator always is).
But I've never had any extra gunk left over from my tried-and-true method... just saying. ;-)
Keep this in mind when removing the price tags over the next few weeks as you prep for the holiday!