I haven't done any riding on the Western slope, but I can highly recommend the Peak-to-Peak highway on the front range (highway 72).
If you're taking 285 you can take I-70 east to 72 which takes you on a really nice, curvy, scenic road all the way up to Estes Park. If you're traveling after Memorial day, you have to take the road up to the top of Mount Evans. It's south of Idaho Springs off I-70 and is the highest paved road in North America. Goes up to over 14K feet and is only a short detour off the main road. My K1 has made it twice with no problems.
When are you coming through?