Some people have suggested corns, because corns are great snakes. I've kept corns in the past, but I just like others better personally. If corns interest you, Kings and milks are a great option to look at as well. I'm personally a huge fan of Kings.
All three colubrid species above are very easy to keep and popular in the pet trade for that reason, plus they remain a very manageable size.

If you go that route, be sure that your enclosure is 100% escape proof. These guys are escape artists who could put Houdini to shame. They're very quick and can fit into the tiniest of places and be gone forever....just a heads up.