unix commands

awk..........pattern scanning and processing language
bash.........the Bourne Again Shell, the only shell you'll ever need
cat..........`concatenate', sticks files together or displays files
chgrp........CHanges the GRouP ownership of a file
chmod........CHanges the permission MODe of a file
chown........CHanges the OWNer of a file
cp...........copies files
csh..........a wimpy shell; avoid in favor of tcsh
date.........print or set the system date and time
dd...........copies a file, optionally skipping bytes in source or dest or doing conversions
echo.........outputs a line of text
ed...........a line editor nobody uses if they can help it; good to know, in a pinch
false........outputs nothing and returns 1
file.........tells you what type of file something is
grep.........pattern matching utility; few commands get more use
gunzip.......decompresses gzip files; same as gzip -d
gzip.........compresses/decompresses gzip files
hostname.....tells you your computer's hostname
kill.........sends a signal to a process; default, of course, is the kill signal
ln...........create hard links or symbolic links (soft links) with -s
login........run by the system on unused terminals; permits a user to log in
ls...........lists files in a directory, 100 different ways
mail.........utility to send and recieve e-mail; has no UI to speak of
man..........the online manual; allows you to view man pages (manual pages) for commands
mkdir........makes a directory
mknod........makes a special file, usually a device file or a named pipe
more.........a pager; it lets you view files or program output a page at a time
mount........makes filesystems accessible by attaching them to mount points
mv...........moves files around in the filesystem
netstat......gives information about sockets listening and open connections
nice.........runs a command with a lower priority than normal (or higher, for the superuser)
ping.........sends ICMP ECHO packets to see if a host responds, which usually tells whether it is up
ps...........gives a process list, for your current session or the entire machine
pwd..........tells you your current directory
rm...........deletes a file or group of files, or a whole directory tree
rmdir........removes an empty directory
script.......makes a typescript, a record of an interactive session, and saves it to a file
sed..........Stream EDitor which is used in pipelines to change text on the fly
sh...........the original Bourne Shell; now usually a symbolic link to bash
sleep........waits n seconds and returns
sort.........alphabetically or numerically sorts its input
stty.........changes the properties of your terminal
su...........allows you to become another user, with their password
sync.........writes filesystem changes to disk; good idea just before trying something boneheaded
tar..........Tape ARchive, not used as much with tapes anymore; makes many files into one
tcsh.........improved version of csh; some prefer it to bash, for various reasons
touch........create a file, or change a file's last modified time to now, or to something arbitrary.
true.........opposite of false; returns 0
umount.......removes a filesystem from its mount point, making it inaccessible
uniq.........prints out its input, removing consecutive duplicate lines. Useful in combination with sort.
vi...........good editor, one step up from ed. Many prefer emacs or pico. Make your own decision.
yes..........outputs endless streams of "y "; useful when piped to a command asking yes/no questions
zcat.........unzips an archive and outputs its contents

Note that these are not, by any means, all the useful UNIX commands; they are, however, some of the most important ones IMHO. /msg me if I've forgotten anything critical. Of course judgement is involved in deciding what goes here, and I don't think mine is necessarily any better than yours; please /msg me rather than flame in the node if I have left out your favorite editors/commands/whatever. I will add, within reason.