I just came across the Internet Developer site at Apple, a great resource for figuring out how all the critical web tools work and how to get them to work under OS X. If you're a developer, or you just want to add a ton of power to your Mac's software capabilities, be sure to check out the Web Development and Mac OS X section. It covers installing and using such things as perl, php, mod_ssl, CVS, and has a great article on open-source databases.

(Reminder to Apple: MySQL by default, right?)