Candy Bar - lets you change icons including ones on the dock
Snood - game, time killer
Adium - chat client, does aim, gchat, msn, etc.
Growl - comes with adium does notifications in the corner
iStat - runs in your menu bar and gives you system info like cpu use, mem use, hard drive space available, temps, fan speeds, etc
App delete - when you delete a program on a mac it normally leaves files behind, use this and it gets everything
VLC - video player that does wmv and other formats quicktime doesnt support
Everything is free except for candybar and that only $30.
anybody got an ipad? the consumer in me wants one baddd