For $8 at the local office supply store you can buy a plastic container that in five minutes with a soldering iron, you can turn into a cage that will house a snake 3 times the size the largest kritter keeper will hold.
www.madprogrammer.com/snakes/handling/
But to answer your question, reingnecks and Dekay's snakes stay very small, but neither are really good first snakes. You could always get a Brahminy Blind Snake, but it might crawl through the air slots in a kritter keeper...
I can't think of any good choices that stay that small.
Maybe a male kenyan sand boa? What size keeper are you talking about?
-----
What goes up must come down...unless it exceeds escape velocity.