I would have to say the corn as well. Being diurnal (I swear I read that they mostly are diurnal... ) mine was often seen basking and cruising his cage, hanging out in his plants. Great animal to handle, very curious about their surroundings and alert.
Other than a corn, I'd have to say a black Mexican king snake, or Honduran milk snakes are at the top of my list. But I really do love the corns and rats.
If you want a sort of exotic rat snakes species, check out the Blue or Vietnamese Beauties.