I am currently sitting in the San Jose airport waiting to board my plane and as taking advantage of the free wifi to putz around on my mac. Here a couple fun terminal commands that I just ran across:
1) say hello
just type say and then whatever else you want and your mac will speak to you.
2) telnet towel.blinkenlights.nl
allows you to play Star Wars IV (all in ascii) on your mac. Someone had way too much time on their hands.
for these and more, check out: http://www.mactricksandtips.com/2008/02/top-50-terminal-commands.html