Corns or most any king snake are a good bet though I would avoid grey banded kings as they are temperamental feeders. If you can take something a little larger ball pythons and woma pythons make good pets. Big noodles, mellow disposition. Minimum space needed for them is something along the lines of a 41Q tub or a 55G tank. They'll eat small-medium rats as adults but can easily be worked onto freeze/thawed food (all of my snakes are on F/T.)
Another possibility would be Kenyan sand boas. I have never kept them but they have a big following in herp circles and are supposed to be uber easy. Just give a simple cage and enough substrate to burrow through.
Things I would avoid would be the mega snakes (Burms, Retics, BCI/BCC), highly active types (Morelia genus) and arboreal snakes.