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.