I love progressive bands like Crimson Glory, Queensryche and Savatage. They have some monumental albums in the 80's and some excellent and shit ones in the 90's. Other similar bands worth mentioning are Dream Theater and Fates Warning, but I wish they had better vocalists.
From the more heavier stuff I like mainly extreme bands like Cynic, Agalloch and Atheist, doom bands like Solitude Aeturnus, Novembers Doom and power/trash bands like Sanctuary/Nevermore, Megadeth and 80's Metallica.
I really dig Anacrusis, Faith No More, Galactic Cowboys, Voivod, Thought Industry, those bands defy classification so I put them seperately.
I also still listen to some grunge bands, mainly Soundgarden, Pearl Jam, Stone Temple Pilots, Alice In Chains and Nirvana - these basically turned me into heavier music..
Outside of metal I like Depeche Mode, REM, Tori Amos, Doors, Pink Floyd, and many others...
Overall there are a lot of great bands from the USA and it's really hard to pick only one.. But if I have to choose two bands that would be Crimson Glory and Anacrusis, the first had the greatest vocalist ever born, and the second is the most unique thing I've heard.