I know this will freak some people out, but rats are great! It was the bane of my childhood that my mother wouldn't let me have any rats.
One of the boys in the neighborhood had Norwegian Fancy Rats, and we had a BLAST with them. His dad helped him built a habitat for them that went all over one whole wall of Shane's room, plus they built a Skinner-type maze with moveable walls out in the garage that we could run races with them in. They were really affectionate, and loved to ride around on your shoulder and they learned all kinds of tricks, like giving kisses, and riding the dog. They were just enormous amounts of fun. Shane's dad would usually allow 1 litter a year, and there were ALWAYS kids left crying because there weren't enough kits for everyone that wanted one.
I've considered several times getting a couple of rats. The deal breaker for me, and the one thing I would caution you about, is that properly done their habitats take up a LOT of space. And I have too many shelves full of books to make room for a habitat.
Norwegians do get pretty big--like 4-6 inches without the tail, a literal handful--and IMHO they're generally sturdier than most rodent pets--they have that cat trick of landing on their feet when dropped, so they don't get hurt as easily as a hamster or a guinea. But you shouldn't get just one, really. They're very, very social, and can be very attached and attentive if properly raised, but can get a little neurotic if they don't have a companion.
