I'm cheap so I soak the bottles in warm, slightly soapy water using dish detergent. After an hour I take a butter knife or a paint scraper and take the labels off. Then the bottles go back in the solution for 10 minutes or so. I get the remaining labels off with a green kitchen scrubby.
So all you need is the detergent, a bucket, a paint scraper, a green scrubby and some time.