I just upgraded to a newer, faster iMac which gave me an opp to clean out all the crap programs that had amassed on the old machine. After a bit of research, here's the essential apps that made it on to the new machine (aside from the preloaded stuff):
Adobe CS4
Adium
Canon Util (for digital SLR)
Firefox
Cooliris
Evernote
Flickr Uploader
Flip (for Flip HD recorder)
Handbrake
VLC
Quark7
Quicksilver
Toast 10
VisualHub
VMWare Fusion + XP
Vuze
Tweetdeck
Meta-X
iWork
iLife
That's it... all the rest are browser/SaaS-based tools that required no install.