Benelli (part of Beretta, makes shotguns and weird looking rifles)
Kel-Tec (makes small handguns, semi-auto rifles [including a "pistol" that's just a radically shortened rifle with no stock], and everything's polymer)
Springfield Armory (one of the few companies that still makes M1 Garand rifles, it also makes 1911 clones, the XD [pretty much a Glock with an extra safety], and M1A rifles [semi-auto M14's])
NORINCO (big Chinese company that makes everything from replica 1887 lever-action shotguns to AK-47 clones, weapons made by them can't be purchased directly from them in the USA but are common used, sometimes imported from Canada)
Glocks come in these calibers: .380 (Not in the US for a very weird reason), 9x19mm Luger, .40 S&W, .357 SIG (around the same power as a basic .357 Magnum cartridge), 10mm Auto, .45 ACP, and .45 GAP (pretty much a shortened .45 ACP).