This is just a listing of some of the administrative tools I have on my *nix systems.
PowerTop - a great utility that shows power usage by process.
bwm-ng - Live bandwidth monitor for all interfaces
iptraf - interface traffic, with option for sort by MAC
iftop - simpler graphing & text of transfer by host pair
jnettop - yet another traffic by host pair, text only
nload - simple statistics by interface - use interface as command-line arg
netstat -lnp - shows all processes listening on ports and sockets