linux has a long history of making available cheat sheets for their command line based programs. Basically it's (meant to be) a single sheet of paper with the most common/useful commands and parameters. Including usually a ton of useful tricks you don't know by heart. (eg how to jump to the beginning of a line in command line, delete the last word, etc)
As I was looking for several this morning, I figured I'd share the ones I finally printed out. They're really cheat sheets with the exception of zsh where the shortest cheat sheet I could find was 7 pages long. :rofl:
bash/zsh cheat sheet:
http://www.cheatography.com/davidsouther/cheat-sheets/bash-zsh-shourtcuts/pdf/
zsh cheat sheet:
http://zsh.sourceforge.net/Refcard/
vi cheat sheet:
http://linux.subogero.com/1020/vi-cheat-sheet/
I figured those might be useful to others as well. If you have more of those, feel free to add them.

regards
myrti