I keep returning to animal care. My first job was dealing with cats and dogs boarding in a vet's office. several years after that, I worked in a pet store with puppies.
Eight years later, and I get another pet care job. This time it's the overnight shift. :-p
Me, my co-worker, and the animals. And the animals are really the best customers out there. It can be messy, and it can be smelly, but I got over that because the dogs and most of the cats show a lot of appreciation for all the little things you do for them, especially when they're new and scared. Some people who shop retail would find something to call your manager for even if you handed them a million bucks on a silver platter.
A quieter, mom-and-pop type retail place is good for practicing with people while being less mobbed than at a walmart. I worked in a small gift shop for awhile, and the lady who owned it was one of those free-spirits who had no issues with my oddities.
edit - i've always wanted to work in a book store, but never got the chance. they can get pretty busy, but it's a different type of crowd.