Check out Pri-Paired firearms in Lafayette: http://www.pri-paird.com/
I did an FFL transfer through them and they gave me a great deal on an EoTech, great staff, mostly infantry Vets.
There is a Jax outdoors right down the road from them, but Jax stopped carrying any magazine fed rifles last year.
GunSport in Boulder is pretty decent, great used selection. You're not too far away from the Cabela's in Thornton, but they really don't have anything that the smaller guys don't.
