Lynda.com

I know that I posted about this a few weeks back, but I want to give another plug to Lynda.com for their PS tutorials. I just finished a 12 video series on sharpening in CS4 and was amazed how much information was contained in the tutorials. I started another series on color management a week ago and have only been able to get through about half of the 40+ videos in the series. That's how these courses and video series are--very thorough. The information is incredibly in depth and dives into the mechanics of how each tool and feature works, which is important to understand, I think, if you want to become a capable PS user. It covers all editions of PS back to 6. And, despite the stern vibes the sideburned librarian is shooting off, the instructors are all entertaining to listen to. This site is the go to site for PS info.

If you don't have access to it through school, work, or whatever, I think it is worth the $25 a month if you are serious about getting better at PS.