Probably the biggest that I can think of is Mountian Air Cargo, they fly F-27s, C208 and I think SD330s, for FedEx. Others include Superior Aviation-Metros for UPS, Wiggins C208s for FedEx and BE99s for UPS, Air Cargo Carriers flys SD330s and SD360s for the Post Office. I flew EMB-110s for a smaller company that flew UPS freight. Pay was poor at best, I worked four days a week and flew about 1.5 a night and was on duty sitting in a UPS crew room for about 10 hours a night. I had no benefits, the equiptment was old, and we had to unload our own freight. At my pax regional the people load themselves, I have great benefits, I fly a nice new jet, travel passes for me and my family, and I make a little less money as an FO holding a line, than I did as a Capt flying freight. Not all freight companies are this poor, I just worked for a bad one.