i'll add a few of my "must have" and "nice/fun to have" resources to Paul's list:

• MacMinute: more frequently updated than MacCentral and MacNN and just as good
• Mac OS X Hints: seems to have something useful every day
• MacSlash: predates apple.slashdot.org, so it's got a personality all its own
• O'Reilly Network: Mac DevCenter: not super-frequently updated, but always carries interesting stuff for even the most casual Mac OS X developer
• Mac OS Rumors: they usually try to pass off pure speculation as reliable information, but it's fun to try to guess when the next CPU will come from Apple
• Think Secret: often better-founded gossip (ie, developer seed builds of applications, etc)