Searching on
http://www.macupdate.com/ or
http://www.versiontracker.com/macosx/ should find most of what is below and saves me hunting up links...
General
QuickSilver - A launcher and more, much more
SubEthaEdit - Nifty text editor
QuickSilver
Mac The Ripper - DVD ripper
QuickSilver
Synergy for iTunes - Add on for iTunes
You get the idea
Camino - Browser
Skype - IP phone
Adium X - Instant Messaging
Slightly Eclectic
ShapeShifter - Appearance customizer (not Free)
VLC - media player
Handbrake - Video Encoder
VoodooPad - NotePad with Wiki-like functions (not Free)
Stickybrain - Personal Organizer (not Free)
PithHelmet - ad-blocker
Virtue - virtual desktops
NeoOffice - Mac version of OpenOffice
DVD2OneX - Encoder (not Free)
Basic Geek Chic
Carbon Copy Cloner - copy your drive to another drive
Geek Tools - display things on your desktop
Audio Hijack - redirect sound output (not Free)
OSXVNC - remote access server
Chicken of the VNC - remote access client
Yasu - maintanence utility
Cocktail - a different maintenance utility
EDIT: added a brief description to each.