JAX is pretty good, although kinda pricy at time. They've got a new guy in the guns dept., whose getting them more focused on milsurp and milpattern guns, and there are deals to be had now and again. Good folks and a pleasure to do business with.
On College ave in "oldtown" there's Cache La Poudre Rifle Works. Best place for "true" transfers as their transfer fee is low and they're good folk. I think they do a markup on transacitons that arent' really a transfer (i.e., you're ording from a distributor), but I don't blame them.
Hamblin Sales is out on Mulberry close to I-25 on the south side. Pretty good selection, especially of nice shotguns and handguns, but I've never been too impressed with their attitude toward military pattern guns. There's a lot of "pucker" factor just to get some help, in my experience.
Jensens' down in Loveland is high speed, low drag for all your evil black rifle needs. They're a cop shop, but they're not dicks to the good guys who arent' cops. Good selection, decent prices, lots of ammo, and they'll order you 'bout anything. They will transfer in anything they don't carry, but they charge a higher transfer fee.