A-Basin
Arapahoe Basin- the elevation here allows skiing (frequently) into July, and beyond! This area can get a tad chilly on top!

Beaver Creek
European Village setting "upscale skiing experience" (from snow.com)

Aspen
To me, if you haven't done Aspen Mountain, you haven't skied Colorado. "Ruthies Run" may just be the premier (and most famous) intermediate run there is. Also includes Aspen Snowmass and Highlands.

Breckenridge
A pleasant hour and a half from Denver- if the weather be good! (from snow.com)

Cooper
Near Leadville, Ski Cooper was the stompin' grounds of the famous 10th Mtn. Division of WWII., whose ski training was largely done here.

Christy Sports
With locations (several) in Denver and at all the major areas, Christy is a good source for those who choose to rent equipment. Online reservations available.

Keystone
"Premier Family Resort." Night-time skiing is featured at this huge area.

Loveland
At the Continental Divide. Great snow, and easy to get to from Denver, as you don't have to cross any passes. A favorite of local skiers, including me- I learned to ski at this area.

Sunlight
Don't overlook this gem! Stay in Glenwood Springs, ski Sunlight, drive to either Vail or Aspen to ski- and there's always the Hot Springs pool. A real bargain for family skiing!