I have a tub that's been filled with water and oxiclean for about 2 weeks. Anytime I've come across new bottles, I just toss them in there and forget about them. After a few days, I come back and all the labels have fallen off. When I pull them out, I use a towel to vigorously dry them off to make sure all the adhesive (which now feels like jelly) comes off. It's super simple and pain-free.
If you're in a rush, you can use much hotter water. I've seen the labels fall off in as little as 6 hours using that method.