Not sure if this website was posted here before. I've had it in my Bookmarks for a while but I use it as reference from time to time whenever I see a picture and wonder how to achieve the same effects. The difference between this one and websites like, say abduzeedo or nagivity is that it's focused on photography and one of the basic differences is that in this field, it's better to do as little editing as possible to get the desired effects because nothing beats naturally-achieved ones.
http://1x.com/tutorials