Linux (and other *nix variants)
nmap <> best port scanner out there
BitchX <> best IRC client out there
eggdrop <> Bot
oidentd <> so you can have identd behind ipmasq
VNC <> in case you need to access a pc across the network, and you are too lazy to walk
snort <> good sniffer
Windoze
SecureCRT <> my favorite ssh/telnet client
VNC <> in case you need to access a pc across the network, and you are too lazy to walk