Off the top of my head:
American: Kolar, Remington, Winchester, Colt, S&W, NEF, Smith-Corona, Springfield Armory, DPMS
Italian: Beretta, Benelli
German: SIG-Sauer, Walther
Misc: Browning (Japan), Browning (Belgium), Sako, Taurus (Brazil), CZ
Based purely on manufacturers, it's 50% US, 50% foreign.