Forumberichten van rainingdarkness

Love the Proko videos, super helpful!

http://www.conceptart.org/forums/
An awesome site with many dedicated and professional artists, the best part is the sketchbook section. Be sure to be ready for criticism there, but if you really want to improve, it's got the best environment I've found for it!

http://www.fineart.sk/photo-references/andrew-loomis-anatomy-books
Copies of Andrew Loomis' anatomy books. I think they're all out of print now so they're free for use.

http://www.boneclones.com/human-analysis-reports.htm
Lots of human skulls to reference, good for learning the proportions of the face.

http://purplekecleon.deviantart.com/art/How-I-See-Color-A-Tutorial-184642625
Great tutorial on color.

http://majnouna.com/tutorials.html
Pretty awesome site with a lot of useful tutorials.

Nude models are best for learning anatomy, however if you're uncomfortable looking at photos of real nude people, you may learn better from an artist's book on anatomy. I don't really think you'll get a good grasp of it by looking at clothed people. You need to understand what's underneath to learn how to properly place the clothing, anyhow.
This book might help you: http://www.scribd.com/doc/4437416/loomisfiguredraw