If you're traveling between the major towns, Greyhound is your best bet. In Crested Butte, Mountain Express shuttles regularly between the town and the ski area every 15 minutes during ski season. The Galloping Goose loops around Telluride every 15 minutes in summer and winter, less often in the off-season. Durango Lift has regular bus service up and down Main Street, as well as to Purgatory during ski season.
Durango Lift (970/259-5438). Galloping Goose (970/728-5700). Mountain Express (970/349-5616).