As far as Colorado goes, and Denver specifically, the Cherry Creek area is a great location. In addition, I've seen a few very nice cars (just yesterday I saw a Gallardo, a Testarossa, and a Viper) on C-470, and of course, as expected because it's an interstate, I-70 is great too. As for Colorado Springs, it's tough to narrow it down, though the street Nevada, which runs through a lot of Colorado Springs, is a good place. Especially south Nevada. The other great place there is the Broadmoor area, whether it be at the hotel or around the neighborhood.

Edit: benb04 has a great point with some of his places too, and he sounds a little more experienced than I am. I especially agree with Vail and Aspen.

Old time Peal is good on Fridays and Saturdays (saw 12c Gallardo, F430, Cerrera Gt), Cherry Creek Valet, Park Meadows Valet, Parts of Colorado Blvd. in or by Barns and Noble/Game Stop, I-25, Old town Littleton, University Blvd and Evans, DU Area, Cherry Hills, Vail, Aspen, the Four Seasons Hotel valey (saw an SLR), Larimer Square...that's all I got.

Incredible spot! Could you tell me some of the better spotting location in any area of Colorado?