This picture was a drawing exercise assignment from one of my architecture classes.  Our professor asked us to find a picture, cut it in half, and draw the other half, it didn't have to be a person but that's what I chose.  This picture is from a photo I took of my friend Leah Jones, and I've always thought she looked beautiful in it, so it was a lot of fun to draw.  Even though it took a while it was really remarkably easy, all I had to do was duplicate what the other half of the drawing looked like.  I'd say this is also a pretty good technique for learning how to draw things, be it faces or anything else, though it works much better when you're drawing something symmetrical.