FireFox 3 to start (although Safari is getting there).
Adium ( for all your chatting needs)
BOINCManager (so you can run SETI programs as your screen saver!)
ies4osx (if you do any web development it’s nice to have for debugging)
iRachet (great invoicing program)
VLC Player (great all media player)
Tomato Torrent (for all your bit torrent files plus a great name)
Pixelmator (instead of photoshop, and is coming along nicely)
Handbrake (useful for pulling apart DVD’s)
Flip4Mac (nice utility for changing those pesky Windows Media Player clips on websites into quicktime, works on the fly in websites)
Hope that helps – that’s not even getting into the great games you can play on OS X: Diablo II, StarCraft 1, Warcraft 3 :p