For my next set of cycling glasses, I plan to buy some sunglasses with prescription "transitional" lenses -- the kind that change from clear to dark, depending on light conditions. I think that would be the perfect solution for commuting because it's usually dark when I ride to work in the morning, but bright in the afternoons. Right now, I carry a couple sets of eyeglasses with me each day, but I could get by with one pair with the transitional lenses.