From Apple's website:
Apple's main Support page.
Apple's iBook G4 and PowerBook G4 Battery Exchange Program.
Apple Mac OS X Updates.
Apple Discussions.
Apple Downloads.
Apple MobileMe Tutorials.
Apple Tiger support.
Apple Leopard support.
Apple iMac support.
Apple Portables support.
Apple iPod service and support.
Apple iPhone support.
Apple iTunes service and support.
Apple iPhoto support. And iPhoto Multimedia Tutorials.
Apple iLife '09 Multimedia Tutorials.
Apple's Mac 101 "Get started with the Mac" tutorial.
Apple's Switch 101 "Migrate to Mac" tutorial for PC switchers.
Apple Product Documentation.
Other sites:
Versiontracker for Mac OS X - for software updates, shareware and freeware.
TeachMac - a searchable library of tutorials built by Mac users for Mac users. TeachMac is not free but is a good value.
ScreenCastsOnline Video Tutorials - "free video mac tutorials to help you get the most out of your mac."
MacFixIt - "Troubleshooting Solutions for the Macintosh."
Microsoft mactopia - Mac support for Microsoft Products.
Mac OS X Hints.
A great Mac community site
and also an entertaining and informative Mac podcast.