I have made several linux cheat sheets to speed up the learning process of some tools.
Recently I decided to put them on my blog.
Here is a link to all the cheat sheets on my blog:
cheat sheets at catonmat (my blog) 
* awk (awk, nawk and gawk) programming language cheat sheet ,
* sed, unix stream editor, cheat sheet ,
* ed, interactive unix text editor, cheat sheet ,
* perl's special variable cheat sheet ,
* perl's pack/unpack and printf/sprintf function cheat sheet ,
* screen vt100 terminal emulator cheat sheet ,
* bash vi editing mode (readline) cheat sheet , and
* bash emacs editing mode cheat sheet .
* definitive guide to bash command line history (with cheat sheet) .
Tell me what you think and I hope you find them useful!
ps. I have 5-10 more to publish, if you are interested, check back and possibly subscribe to my posts via rss feed