Thracian:

There are a few sites like:
http://www.the-blueprints.com/index.php?blueprints/humans/humans/

But I strongly recommend to practice drawing your own reference pictures. It teaches so much about the object. You learn the terrain of a face very good when you try to sketch it first. It even helps to get an idea of a good polygon-flow.

Just modelling from a sketch is a start but will not lead to professional models.

I wish you fun and much success!

Regards,
Frank