I ordered a pair of prescription sunglasses from Eyefly.com through a great deal on Living Social. ($49 for a complete pair of glasses, shipped.)
That was pretty cool, but this is even cooler:
While browsing for glasses on Eyefly, you can take a photo of yourself with a webcam. The site uses software that will automagically place a 3D rendering of the glasses on your face so you can see how they might look. (Adobe Flash required.) :P
The software isn't perfect, as it automatically adds mirrored tinting to the sunglasses, but the "fit" is pretty good. See the photo above.
(No, I hadn't yet shaved. Or showered. Just ignore that part.) ;)
This is an excellent tool for selling a product online that people typically prefer to first try on. To add to shopper's comfort level, they also include Zappos-style free shipping and returns.
I will most likely get another pair from Eyefly because of this crazy-cool feature. (Though I wish they would allow me to add sunglass tinting to a regular prescription frame.)