A western Hognose. They all have great personality (there is no other snake in the hobby that does what they do), look beautiful (the normals are great, but you should see the albinos), and are really easy to get (at an expo at least. They're practically inexistent in pet stores for some reason even though they were one of the 5 snakes widely available 25 years ago). Males grow really small (rarely exceeding 20 inches) but females grow up to 30 inches (and are much more stockier than most other 30-inch snakes). You could basically call the Western Hognose snake the "Colubrid double" of the Kenyan Sand Boa.
EDIT: Man, besides for DSGB and I, no one mentioned Hoggers! I'm glad I got this post through.