I wouldn't mind living in a college town...Boulder, Fort Collins and Denver are the 3 biggest right?

They are 3 of the 4 largest cities. The Univiersity of Colorado at Colorado Springs would have to included and the Air Force Academy is also there. Colorado Springs is one of the largest cities in Colorado. In my opinion, if you are talking about living in a college "town" Fort Collins and Boulder would be the two you might consider, but you also have UNC in Greeley, School of Mines in Golden, Colorado Mesa University in Grand Junction, CSU Pueblo in Pueblo, and Western State in Gunnison. All offer great experiences and are super college towns.

I can vouch for Gunnison. I went to Western State my freshman year of college and absolutely loved it. If you like a smaller town atmosphere at all, I would urge you to check it out. The scenery is beautiful, the people are so nice, and the atmosphere is laid back and casual.