Hair magazines are often quite good for inspiration. I sometimes ask clients to cut out pics, if they like the back, sides or fringe of a pic, then I draw a picture of how it will look all put together. It's difficult to find a perfect picture to show a stylist and say 'I want it exactly like that.'
I gather there's an iPhone app that shows different hairstyles, but I don't know the name of it off the top of my head.