I found Michael Hampton's (I wrote about it in my article Anatomy resources for self-study ) book is perfect for start and good understanding what you do and why.
For reference, if you don't have access to model in studio, you can go to one of those websites:
Alternatively, you can collect your own folder with nice photorefs and play them slideshow with time interval set from 30sec to 3 min. I use FastStone Image Viewer it's free and have all functionality that I need.
Good video tutorials:
http://www.youtube.com/watch?v=QMlzkZH_4LI&list=WL1BE0B05E656878C8 (more cartoony approach)
Some inspirational sketches:
That one from Ryan Woodward he's awesome!
And a few more,I collected them some time ago, so don't know whose they are