Big Bag'o'utilities

All utilities listed below are command line utilities; install them using apt-get install or aptitude.

apticron checks your system daily, and mails you when there are updates for packages
bzip2 is a file compressor/decompressor
ccze can "colorize" output, e.g. tail -f /var/log/syslog | ccze
ipcalc is an IP address/mask calculator
( iproute helps viewing and setting the IP configuration - under Lenny it's installed by default, under Etch you'll have to do it yourself)
iptraf is an IP traffic monitor
less is a utility to view text files;
pwgen is a password generator sudo enables you to execute commands with another user's credentials
tcpdump is a network sniffer
arj is a file compressor/decompressor for the .arj file format
unzip is a file decompressor for the .zip file format
unzoo is a file decompressor for the .zoo file format