Here are a few that I have really enjoyed. About half the passes in Colorado...I have done 2-Up with the wife and we had a blast!!!
By the way, if you are willing to tackle some rough and tough dirt, I would highly, highly recommed the San Juans in the southwest part of the state. Not only is there great dirt passes, but also amazing pavement passes. By the way, this is the location of the 2009 Colorado Strom Gathering.....Ouray, CO!!!!!
Loveland Pass. Paved road. Well maintained in the winter. Fun Twisties...piece of cake to ride. 5 on a scale of 10.
Owl Creek Pass (10,114). Maintained Forest Service Road. Not sure about winter access. 6 on a scale of 10.
Cinnamon Pass (12,620). (Roughly) Maintained Jeep Trail. Closed in Winter. 8 on a scale of 10.
Marshall Pass (10,842). (Roughly) Maintained Forest Service Road. Not sure about winter access. 7 on a scale of 10.
Hurricane Pass (12,407). 'bout the same as Cinnamon.
Kebler Pass (10,007). Maintained County Road. 6 on a scale of 10.
Monarch Pass (11,312). Highway 50....easy going. 5 on a scale of 10.
Cumberland Pass (12,015). Roughly maintained Jeep Trail. 7 on a scale of 10. Did this one 2-Up!!!
Other passes done on the Strom that I would recommend (no pics, sorry)....
Engineer Pass (12,780). Jeep Trail...very little maintenance. 9 on a scale of 10.
Highway 550, "Million Dollar Highway". Molas Pass (10,910). Coal Bank Pass (10,640). Red Mountain Pass (11,018).....all great pavement and easy ridin.... 5 on a scale of 10.
Wolf Creek Pass (10,810). Highway 160. Paved and easy stuff. 5 on a scale of 10.
Independence Pass (12,095). Highest Paved Pass in North America. 5 on a scale of 10.
Hoosier Pass (11,539). Paved Pass. 5 on a scale of 10.
Trail Ridge in Rocky Mountain National Park. Iceberg Pass (11,827). Paved, but Closed in Winter. 5 on a scale of 10.
Yeah....there are many, many, many more........
By the way, the only reason I rate the paved passes a 5 is because of the sand and gravel on the road in early spring...possible ice in the shady spots. In the summer, they are an easy 3 of 10.
I know about tons more. My three year goal is to ride every pass in Colorado and I am about 2/3'rds finished. Summer of 2009 will be a BIG year of Pass Riding.