I use PaintTool SAI. I start off with the whole hair layer one solid shade, then use my paint brush tool set to Flat Streak and start highlighting areas. To mix things up a little I use a brush shape called GrassEm01 for finer streaks of hair. To top it off, I use an overlay layer or two to give areas a shine. I've been meaning to make a small tut on how I do things, but I end up getting self conscious about it..
I can't get PaintTool SAI. It's for Window computers and I have an Apple computer. Thanks. It'll help me a lot! And you should make a small tut because the way you draw the hair is the reason I follow you.
Photoshop is also expensive. PaintTool SAI seems to be much better than photoshop, I've watched a lot of speed paints of people drawing ponies with PaintTool SAI and they are amazing! I wish I could get it.