unix commands

I know some basic unix things, but I know there's a lot more out there.  Anyone care to share some of the things you find useful?  I basically only use these commands so far(and pipes and subcommands with $): cd, ls, chmod, mkdir, rmdir, rm , mv, cp, cat, less, grep, wc, find.

some things I like so far:
"cat file | less" is pretty cool for instant file viewing
"grep anything" grep rocks

cat file | less
And of course, if you've been following along for a week or two, you know that this (BING!) is a Useless Use of Cat!
Remember, nearly all cases where you have:
    cat file | some_command and its args ...
you can rewrite it as:
    <file some_command and its args ...
and in some cases, such as this one, you can move the filename to the arglist as in:
    some_command and its args ... file

Just another Useless Use of /prog/