I've been wearing contacts longer than I've had my bike -- didn't realize regular glasses are not so good at protecting your eyes when you ride.

I find the interchangeable lenses on my sunglasses are excellent. I can get away with dark lenses (I highly recommend polarized lenses) for most conditions plus a pair of yellow ones for riding at dusk. If you ride in the dark you might want clear ones, too. Although I find the yellow ones actually brighten things up as the sun sets.