Azureus
Multiplatform Java BitTorrent Client
Desktop Manager
I use Virtue desktops now that it can have one row of desktops.
Gives you the ability to have multiple virtual desktops with different windows on each one, can use the crazy cube desktop rotation for switching.
I use 5, one for Mail + Adium + Azureus, one for iTunes and three for other things; normally a combination of Safari, Terminal, SubEthaEdit and Finder.
SizzlingKeys
I use Quicksilver for this now.
Allows you to control iTunes with global key combinations. Pops up information about new songs.
Acquisition
P2P Music.
LittleSnitch
You can control what applications can access the net. Useful in finding out when an application is connecting to the internet, and stopping it transfer your information.
MenuMeters
Little graphs of your cpu usage and network traffic in the menubar.
MPlayer OSX
Plays movies.
OmniGraffle
Great for making diagrams while in lectures, for software projects, etc. My Powerbook came with this.
Quicksilver
Open any program with a key combination, but much more.
SubEthaEdit
General purpose text editor, great for programming.
NetNewsWire
Excellent rss reader.
VoodooPad
Like your own personal wiki, great for getting ideas out.
Adium
Excellent Multi-protocol messenger client.
Colloquy
Excellent irc client.
Toast 7 Titanium
Burn CD’s and DVD’s
Camino
When I’m not using Safari I use this Mozilla powered browser.
Transmit
Great ftp program.