Boulder isn't a ski resort, so I wouldn't put it on your list of places to ride.
other ones that havent been mentioned are Sol Vista (US mountain bike champs are there this year again) which is just down the road from winter park.
Vail doesnt let you take mountain bikes on the Gondola, so avoid unless you want to pedal
If you're heading to Aspen, I would go to Snowmass instead; quieter, cheaper and the trails are beyond imagination
Crested Butte rocks. go there.
Angel Fire, New Mexico is worth a trip if you're in Southern Colorado, and the Boundary trail which runs from Durango to Angel Fire is amazing.
Hope it helps!
any more info, let me know!!