I have a book I’m working on a review for that I think would be a really useful tool for many artists. It’s called Facial Expressions: Babies to Teens. Mark Simon has put together a huge book filled with head shots of babies to teens from all kinds of angles and with all kinds of expressions. I’ve already put my review copy to use — using it in drawing different characters and adding a bit more variety to how I compose panels.
Here’s a link to Mark Simon’s site — he has created several reference books actually and I’d imagine there all quite useful.