Someone posted this on a different board -- pretty good, just wish they had someone w/ just posing trunks and lean enough to show the pose and what it is activating....
Also on the 'other videos' list on the right side of this page, scroll down & you'll see several sections of a bodybuilding seminar that are useful. They are all posted by the same person - "FitnessAtlantic.com" - you can search on that name as well.
I also like these from Bob Chichirillo (see Posing Part 1, 2, 3, etc.)
YouTube - bob cicherillo posing
Here's another resource I came across on another board. Joe Franco - posing as well as contest prep list / tips (Scroll down towards the bottom for some podcasts.)