I stumbled upon a site called FreewareOSX this afternoon. It catalogs tons of free software available for the Mac. They break it down into sections and give a little description of what each application does.
Here’s some of my recommendations:
Audio/Video:
Flip4Mac
VLC
CenterStage
Communications:
Skype
Thunderbird
Internet/P2P:
Azureus
Camino
Flock
Fugu
Mozilla FireFox
Transmission
Graphics:
Blender
Pixen
Utilities:
gDisk
MenuMeters
Word Processing:
Smultron