walkner.info /articles /My Macosx Must Have Apps

Just enter the program names in a search engine and you will certainly find the right program...

Preference Panes:

Perian: lots of codecs to enable a greater variety of formats in quicktime components
iStateMenus: nice little app that allows to display various widgets in the menu bar

Dashboard Widgets:

Free/OpenSource Programs (not all - just a few I found worth mentioning):

AirStatz: measures the link of your WLAN connection ;)
Lingon: Manage (hidden) daemons (like mDNSResponder [= bonjour] and lots more!!!)
Monolingual: Remove unnecessary languages and processor architectures of applications (saves disk space)
Smultron: Best editor (for scripting languages etc) I found...
MacVim: No comment :D
VLC: watch movies and don't care about codecs etc.
Cyberduck: my favorite ftp/sftp and whatnot client...
Adium: nice multi-protocol messaging client
Growl: awesome and pretty generic notification tool
iTerm: nice terminal application that supports tabs etc.
OnyX: system maintenance and tweak MacOSX
The Unarchiver: embedded in Finder and supports lots of compression formats
Transmission: an awesome bittorrent client (getting better all the time!)
Tunnelblick: openvpn client. Best thing is that you can use your own configs instead of a stupid GUI.
uApp: removes applications (in /Applications) and related files in ~/Library
XCode: great IDE! I really like it... shipped with MacOsX
HandBrake: Rip DVDs easy and handsome