OS X was reently named by the March 2, 2006 issue of Network Computing (p. 54) that "OS X is top-of-the-heap in useability, even beating out Windows." I agree, and sometimes feel that I bear an onerous burden in supporting Windows. So let's have some fun with our Apples tonight!
This web site kinda beat me to the punch and put a lot of great open-source OS X capable applications, including music, web browsing, and a personal favorite - Democracy, which runs on Windows, too. Many of the apps that I am pointing out can also be found here.
The blog, Tao of the Mac, is a bit cerebral for most end-users, but for the techies out there, this guy is good reading.
This site has open source apps for most every platform imaginable - much like Sourceforge, this web site has lots of great multi-platform apps and games. Something for everyone! On the down side, navigating this site can be confusing, and the apps are often very technical in nature.