Back in 2007, I posted a visual hair tutorial
and I feel horrible about it. I feel bad because it's outdated, pretty ugly and has over 7000 views. I'm deeply sorry.
To redeem myself, I created last night a brand new tutorial that shows how to paint semi-realistic hair. To achieve realism, or at least a higher level of completion, you would simply need to add more detail to the hair. This particular hair took me about 15 minutes to do.
If you have any questions or feedback, leave a comment and I'll do my best to get back to you.
EDIT: Wow, just noticed that this tutorial has made it to the first page of popular images for June 6. Amazing. Thanks guys! I'm glad you like it and find it useful