Err the Blog has quite a few application and programming-specific cheat sheets that may come in handy for some of you.

There are cheat sheets on bash, capistrano, chmod, curl, e (text-editor), emacs, markaby (I want to give that gem a go), markdown, radrails_ruby, regexp, textmate_rails and many, many more.

Check out the complete list of sheets at Cheat Sheets