Here's a very basic one I've found. It's main focus is on cars, that might be convenient. http://www.photoshopjunkie.com/tutorials/
For more look into josty's pimpchop thread.
came across this list today on another forum, i guess quite some links will overlap with previously posted ones, but i am lazy to look at all the links and sort them out
[edit] original list i posted removed, i sorted out the overlaps in excel quickly.
ren, why dont you clean up this thread a bit so that only links remain?
so, here's the list i found combined with the one from flipp, out of the ~300links, about 200remained