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
ccze can "colorize" output, e.g. tail -f /var/log/syslog | ccze
ethtool can change settings for ethernet cards, like speed and duplex
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;
lsof can show all open files
multitail can follow multiple (log)files in one terminal
pwgen is a password generator
sudo enables you to execute commands with another user's credentials
tcpdump is a network sniffer
pciutils contains the lspci command, which can be useful to review your hardware

The following are compression and archiving tools: arj is a tool for the .arj file format
bzip2 is for .bz2 files
p7zip is for .7z archives
unzip is for the .zip file format
xz-utils is a toolkit for LZ/M compression; adding it will make tar understand .xz files
zoo is for the .zoo file format