I stumbled across this website the other day, perhaps some of you know about it already. It has great descriptions of the bones, muscles, how the work and other related stuff. Very cool educational piece.
I think this one is better, especially the Exercise & Muscle Directory.
They have nearly every muscle and movement in the body covered and tons of exercise execution moving pictures.
Great for newbies.
I just wish the GIF pics of the exercise executions were in a higher res.