Bands there is a disgusting lack of in this thread.
Cynic - prog metal, and the earlier stuff (Focus and demos) had some death metal in there. Traced in Air is a beautiful album. As a follow up to Focus after 15 years, it was a change in direction from a more chaotic sound, but track like Integral Birth (
http://www.youtube.com/watch?v=pNGCJzPzAp0 ) and Nunc Stans (
http://www.youtube.com/watch?v=gaioYJjq6a0&feature=related ) are breath taking.
Anaal Nathrakh - black metal. Insane stuff.
http://www.youtube.com/watch?v=B6349Q-67eA
The Angelic Process - drone/doom metal. Again, truly breathtakingly beautiful.
http://www.youtube.com/watch?v=TYtQe2XjkQs
http://www.youtube.com/watch?v=pfBd7J75L9c
Amorphis - hard to place, metal just sums it up. Skyforger does not have a track which isn't awesome on it, which is a rare feat.
http://www.youtube.com/watch?v=tf-9MVv_iWo&feature=related
Behemoth - Blackened death metal. Speaks for itself really.
http://www.youtube.com/watch?v=tHhZ2LThpv4
Blind Guardian - power metal. They just destroy the rest of their genre. Nothing else is close to their epicness, or the complexity of an album like A Nigh At The Opera.
Immortal - black metal. Good black metal without being completely up themselves about being "tr00" and "cvlt".
http://www.youtube.com/watch?v=uHSfRpyaIcI
Mastodon - sludge/prog metal. Have tended towards prog recently, but Crack The Skye was just one of those phenomenal albums.
http://www.youtube.com/watch?v=c6Vf5syTfmE
Ne Obliviscaris - prog black metal. I've heard them described as the Cynic of black metal, and it's pretty accurate. Only have a demo out at the moment, but are currently recording an album.
http://www.youtube.com/watch?v=2J7wt2DSQXo
Necrophagist - technical death metal. Just **** good. A bit mechanical, but some seriously sick guitar work.
http://www.youtube.com/watch?v=2SRD6mjrUMo
Nile -technical death metal. Egyptian themed, incredibly heavy death metal.
http://www.youtube.com/watch?v=TpLZi4UrDcA
Opeth - prog death metal. Because there is never enough Opeth.
http://www.youtube.com/watch?v=HmByeB7y5aw
Pleurisy - death metal. Just plain good stuff.
http://www.youtube.com/watch?v=1QsRN32PaTM&feature=channel_page
Satan - NWOBHM. Massively overlooked band from their era.
http://www.youtube.com/watch?v=74Nei5Axde4
Shrinebuilder - doom metal. A supergroup that has just released it's first album.
http://www.youtube.com/watch?v=0MOvk-dNLRY
SikTh - prog metal. Verk weird, but very awesome.
http://www.youtube.com/watch?v=ARTvoqqn8U8
Sleep - stoner doom. Fuzzed out goodness. Not quite as good as Electric Wizard, but dopesmoker (an hour long song) is a journey in itself.
http://www.youtube.com/watch?v=tOpidgBVa5s
Symphony X - symphonic metal. Can be awesome apparently.
http://www.youtube.com/watch?v=GUn4jXZko5E
Wintersun - folk metal. Just one of those bands out of nowhere who produced a masterpiece first time around. The second album (time) is ironically taking ages to be made, but could very well be worth it.
http://www.youtube.com/watch?v=pxMkIm5JxkM
Bit of an epic post, but I think most of those are well worth checking out no matter what you prefer as it stands.