If I may add my 'two penn'orth' to this now unscientific debate, I have to agree with several of the previous posters regarding Serengeti Eyeware.
As a previously 'died in the wool' Ray Ban user, I was given the opportunity to try a pair of Serengeti Lassen sunglasses belonging to a colleague, and I was hooked. I now own a pair of Serengeti Velocity Titanium glasses, with Drivers Gradient lenses. These are photochromic (go lighter and darker with less or more light), graduated so that the bottom portion is lighter...excellent for glancing at the instruments, wrap around so avoiding light leakage at the side (a problem with my Ray Ban Aviators) and coated with a filter which removes the nasty part of the light spectrum that causes damage.
Since using these glasses I have been really impressed with them and find myself squinting less at altitude above cloud and it is so much easier to read the EFIS screens. Colleagues of mine have tried them and bought some (I wish I had shares!).
They come with a beefy case which can withstand most of what hits it at the bottom of my bag. The downside is that they aren't cheap (RRP £170 ish) but try them out in a High Street chain store like Sunglass Hut and then buy them online for big savings (particularly from the States). I bought mine from E Bay. Ultimately, what price do you put on your eyesight? These are good enough to be NASA's official sunglasses of choice, for astronauts.
Have a look:
http://www.serengeti-eyewear.com/dri...gradient_1.htm