Mac Central - Good Mac news site.
Apple Computer's Current Mac parts replacement instructional page - Nicely done, with video, html and .pdf documentation for most machine alterations you'll need to perform. [This material only applies to current Macs: iMacs, G4s, Cubes, PowerBooks, etc.]
MIT's HyperArchive - [http://hyperarchive.lcs.mit.edu/HyperArchive.html] - A no-frills approach to one of, if not THE largest archive of independently released Mac software on the internet.
MacWorld - (www.macworld.com) "THE" great Macintosh magazine. Standard-issue for Mac Nurds. Product reviews, lab tests, tips, tricks, hardware dissections, the works.
MacAddict - (www.macaddict.com) Another Mac magazine, but this one's for the more rabid breed of Mac buff. Focuses more on the consumer [games, kids stuff] as well as some power user content.
MacKiDo - (www.mackido.com) Learn thhe Zen of the Macintosh, grasshopper.
Macintosh News Network - [www.macnn.com] Fresh Mac-related news, 3-times or more daily. A must-read for anyone who needs or wants to keep up with every detail of the Mac world.
O'Grady's PowerPage - [www.go2mac.com/ogrady] The numero uno PowerBook website. Oh, and also mobile computing in general.
VersionTracker.com is an extremely helpful tool for those of us who don't have 8 hours per day to keep up with all the updates to our software. Highly recommended!
MacUpdate.com Very similar to VersionTracker, but Mac-specific.
IconFactory - [www.iconfactory.com] An endless supply of beautiful little pictures to paste onto your own folders and other iconic creations. One of the best websites on the internet for Mac buffs. A long-time gem.
ResExcellence - [www.resexcellence.com] For those who love to mess with all the guts of your Mac's operating system and software. All the stuff you're not supposed to. ;) A fantastic resource for customization fanatics. There's also a small AppleScript Archive!