Another good paved road trip is up the Poudre Canyon from Ft Collins up to Walden, then over to Steamboat. You can come back to Silverthorne, and back to Denver, or take the back way down to Wolcott. Very nice trip!
I agree with every post in here all great places! Also Golden Gate State park up golden gate canyon out of old golden. Been real sandy in the summer the last couple years though, for us motorcyclist.