I've always wanted a rat. I don't know why so many people dislike them.
Bad press. That whole vermin angle...
They really are great pets. They are smart, and you can train them very much like a dog can be trained, and they can be quite affectionate and playful. I used to have several, but I'm on hiatus from rats right now because it is so depressing when they die... which is unfortunately rather quickly compared to other pets. If you're really lucky, they'll live three years.