Julie: Ray Bans are good, if a little cliche'd
they used to be suppliers to the US military I think -a role taken over by Randolph of late. I use Serengeti's. They're brilliant lenses, but the frames tend to be a little weak -you have to look after them: in a case when not wearing them, rather than a shirt pocket! The lenses are photocromatic also. They're expensive, but IMO the most bang for the buck.
Best to stay away from polarised lenses. They create optical illusions in-flight, especially as you pull your aircraft into the flare! Disconcerting!
Comfort is the biggie though -they tend to be worn for extended periods! Have a look at the temples too, make sure they're not too fat as they can destroy the passive noise retention of your headset.