Freshmeat maintains a big index of open source projects, but also includes other stuff. It's basically like versiontracker but with wider coverage (the main focus is Linux, but it has projects for other platforms as well):
You might want to try Fink. I'm really not 1337 enough to describe it accurately, but it's a project that is dedicated to bringing open source programs to Mac OS X. Run the program 'Fink Commander' and you get a list of a thousand or so programs. With a few clicks you can search the list, download and compile the source (including the libraries you need to run them, which was a real pain before I tried Fink) or download updates to programs you already have.
Be warned: as far as I know none of these programs have been ported to use Aqua. Aside from command line tools, you'll need an X11 program to run them. Apple includes their implementation on one of the Panther CDs.
Sorry if I'm not informative enough, I'm not much of a UNIX person. But my point is you don't have to be to use a lot of the stuff Fink is good for.