Ribbon snake. They eat earthworms and minnows, and are usually very docile. They also prefer lower temperatures, are very active, and speaking from experience, a lot of fun.

Also, a lot of the water snakes feed mainly on fish and frogs, they have a very nasty reputation, which they don't really deserve, I've kept several that were very docile.

Garter snakes are also along the same lines as ribbon snakes, and probably the best "beginner" snake out there.

Red-bellied snakes and midland brown snakes are both very similar, they eat mainly earthworms and slugs, but stay very small, under a foot.

Hope this helps,
Kevin