cheat is a very nice command line cheat sheet system.
chit is a git-powered version, that even supports private cheats or project level cheats distributed using the git system.
I've added a bash completion script to chit. It's very simple but it works for me. I've also sent a pull request to robin, so you might see it in the main chit repo in the future.
Update: you can find the bash completion script in the master chit repo now.