I agree w/ catching a game at Coors Field, even if you aren't a big baseball fan, and everything in Thom02099's list (except for maybe Casa Bonita, as the food there is just atrocious). There is also a new outlet mall in Thornton that just opened a few months ago, off I-25 and 136th, if outlet shopping is your thing.
I will also add the Celestial Seasonings tea factory in Boulder. It is really interesting, and if I recall, would be very easy to do the tour w/ someone on wheels. Also Rocky Mountain Arsenal Wildlife habitat out near the airport is very cool, with herds of buffalo etc., and you can do the hour drive loop through it in the car.
And, well, if you all like beer, there's no shortage of great breweries to visit.
