I'll have to second
http://www.uscav.com as they've got good selection, good prices, and are stocked with Airmen Battle Uniform.
http://www.miluniform.com Good place to get the final touches from (great for Gen 2 IR IFF)
http://www.camotech.com/index.htm Great place to get ARPAT custom items (patches, ARPAT flags, etc.)