i second FIREFLY.
just two things about it: one, the pilot might seem a little slow -- don't let that deter you! second, it's a show that rewards you for paying close attention to the dialogue. you won't get nearly as much out of it if you watch while websurfing or doing laundry or whatever.
also, it's quick. a 2 hour pilot, 12 episodes, and a 2 hour movie.