Colorado is famous for it's skiing - but summer or early fall is the best time to visit. It's cheaper and not as crowded. My favorite places to visit in summer are: Boulder, Vail, Aspen, Telluride, Durango, Grand Lake, Steamboat Springs and Rocky Mountain National Park.
If you're coming to ski, the best conditions are usually in February/March, although the snow may be good as early as mid-November. Between Christmas/New Years the rates are jacked up, sometimes doubled. The absolute best day of the year to ski is Super Bowl Sunday - IF the Broncos are playing. When that happens, you will have the whole mountain to yourself.
About some of the Ski Areas: If you want the whole experience, try Vail, Aspen or Steamboat Springs. Each has it all, packaged a little differently. Vail offers European flavor. It is now the largest ski area in America, and it's legendary back bowls drop forever. Steamboat has a western charm to it, a little less pretentious, tons of powder - bring your cowboy hat. Aspen is famous for it's skiing and people watching. A spectacular town, great skiing for every level.
No less great is Summit County: Copper Mountain has great skiing, a Club Med and is a local favorite. It has no nightlife, but Breckenridge and Vail are close. Breckenridge is a beautiful Victorian town with plenty of great restaurants & bars, but it's cold to ski. Keystone has everything, it's a great family resort, and has several mountains of all levels. Keystone/Breck & Copper are all within an hour of each other. Some people who ski these stay in Dillon, which is cheaper and central to all three. Arapahoe Basin is the anti-corporate holdout in Summit County. It's often the last resort open in the state, sometimes you can ski there in July. It's the kind of place where some locals sleep in their car. Brrrrrrrr.
Some other favorites: Winter Park/Mary Jane are excellent, Mary Jane being the best bump skiing around, which makes it a difficult place to board. If you're an expert try Telluride or Crested Butte. Steep & deep.
The photo is of Maroon Bells, just outside of Aspen. More photos in the Travelogue.