I had the good fortune to have Jeffery Scott of Factory 1019 visit me at the studio a few times over the past few years. He is an incredible artist and does some facinating work in Photoshop.
Recently, he released a video series detailing a lot of his Photoshop secrets.
If you are interested in taking your Photoshop to a higher level, you may want to consider this series.
This is a (fast forwarded) sample of the tutorial (contains artistic nudity)