I always say you can't go wrong with a carpet python. Jungles, IJs and Darwins are some of the smaller species. They're beautiful, easy to care for, and they make great display animals. I know you said you don't like colubrids but have you looked at some of the beauty snakes, rat snakes, or Pits (bull, pine & gopher snakes)? What about a dwarf boa?