I have the most excellent sunglasses for running and biking.
They have wide-coverage, brownish lenses, so they're good for lower light and bright light. They're flyweight but sturdy, so I carry them around on top of my head all the time.
I got my first pair at a marathon expo in Memphis three years ago: $25. Liked them so much I bought backups online.
They're the Falcon model from Precision Sport Eyewear in St. Petersburg Florida.
www.precisionsporteyewear.com
I've also got some Smith frames with interchangeable lenses. I use the clear lenses for bike-commuting in the dark and the yellow ones for rain days. But the frames aren't so comfortable as my cheap brownish ones. They're great for almost every day.