This is what I have (others may be useless):
BBEdit - if you're doing programming/editing.
Smultron - Free alternative to BBEdit.
Chicken of the VNC and VNCServer - if you want to access your Mac from elsewhere.
AdiumX - for multiplatform instant messaging
MediaFork - for ripping DVDs/movies
Shrook - News RSS
MS Word/Excel/PPT/Apple Keynote/Pages - Word processing, spreadsheets, etc...
WhatSize - see whats clogging up your hard drive
monolingual - remove around 2gb of unused languages
Transmit - for FTP use
Armagetron Advanced - addicting game
Jumpcut - saves your pastes, so you don't lose them
Google Notifier - gmail notifier when a new email arrives, sits on the bar