Obviously, if you're reading this you already know about one of the main places to read about Aperture, but there are some great resources scattered across the net, not all of which are easy to find...

A good place to start is always Apple's own Aperture sub-site:
Video Tutorials
List of Plug-ins
List of Resources

Then there are several active Aperture forums, apart from O'Reilly's own digital media forum:
Apple's Aperture Discussion Forum
Aperture Users Network
flickr Aperture Users
DPReview Mac Forum - not specifically an Aperture forum, but Aperture-related threads come up frequently.

Articles and Blogs:
This site. ;-)
The Aperture Users Network has a bunch of blogs and articles, plus articles which are only available to subscribers.
Steve Weller's Bagelturf site still has a lot of good information, although most of it is for Aperture 1.5.
RW Boyer is building up a good collection of articles about Aperture, LightRoom and comparisons of both.

Plug-ins:
Apart from the Apple page above, Aperture Plugged In is always worth a look, maintained by our very own Micah Walter.

Scripting Aperture - my own particular interest:
Again, start with Apple.
Next up, John Larson's site is an excellent primer for controlling Aperture via AppleScript, and isn't a bad place to start for AppleScript itself.
Brett Gross also has a large number of scripts that can be downloaded.
Finally, my own Aperture Assistant site has a forum dedicated to Aperture scripting and related subjects.

What other resources do you regularly view regarding Aperture? I'm always on the lookout for more bookmarks...

Ian

EDIT - Ellen Anon's video tutorials on VTC are here.