Rats are fun and wonderful pets! I think the thing that creeps people out, aside from the original thinking of them being vermin, is the tail... once you get past or ignore the tail, they are quite charming.
Incidentally, there are serious rat breeders and clubs that show rats -- they are registered and pedigreed, just like dogs. If you were to buy a rat from such a breeder, it would be on a contract stating that you are buying the rat as a pet and promise not to breed it.
Rats from good breeders are generally healthier and have much better temperaments than those from a pet shop; they are handled from birth and raised to be pets, not mass-produced with the intention of being snake food. Rats from these good breeders come in dumbo ears (large ears on the side of the head) as well as standard ears; rex coat (wavy), standard, satin, or no coat at all (hairless); and wonderful colors like Russian blue, dove, cinnamon, mink, fawn, platinum, chocolate, silver and siamese.
I can't post links because I don't have 15 posts in yet, but google "Ratty Corner" and "Rat Society of America" for more info.