Have you seen this Photoshop tips yet?
oh that's one fact. You'll never know what good it brings till you master them.
that's kind of a vague question, however:
there are a few thousand photoshop tips and tutorials here: http://psd.tutsplus.com/
some are really basic, but many are very cool.
here is one of my favorites by Bill Labus: changing a face to make it look like it made of ribbons of paper
step by step version:http://psd.tutsplus.com/tutorials/tutorials-effects/creating-a-vect...
video version of the tutorial:http://psd.tutsplus.com/tutorials-effects/vector-composite-effect-f...