I've been listening to metal (while acknowledging what I was listening to) for 8 years. Started with Blind Guardian, then I got to know quite a lot of power/speed metal bands. I can't stand listening to most of those bands nowadays, though :P
These are the bands that I've been listening for the past 2 years or so:
Angra: One of the coolest bands from Brazil. They play speed/prog metal. I'm not quite fond of Eduardo Falaschi, tho.
ANIMETAL: It is very hard to stay metal while playing anime/tokusatsu music, and they do that very well.
Anthem: Eizo Sakamoto's band (who is also ANIMETAL's singer). They play awesome early 80s fashioned Heavy Metal.
The Black Mages: Nobuo Uematsu's band. This guy has a respectable mustache and even more respectable song writing skills. Made music for Final Fantasy and Rad Racer (!!!).
Blind Guardian: They might be a little bit to nerdy, but they still rule. Started with some thrash-ish stuff, then moved to a more symphonic-oriented metal.
BrainCells: a Brazilian guitar player who makes awesome metal covers from old videogame music.
Daath: Kind of a mixture of Technical Death Metal with Industrial. Both guitarists are fucking awesome.
Deep Purple: The fact that Ritchie Blackmore is awesome is undeniable. They kick so much ass that it isn't even funny.
The Devin Townsend Band: This guy managed to look cool with a long hair even with a balding head. His music is as awesome as his looks.
Dio: He is the greatest metal singer EVER. Don't you even dare to deny this.
Fastkill: I've only heard one of their albums (I don't even know if they have released more than one). They are a Thrash Metal band from Japan, sounds kinda like Kreator for me.
Five Finger Death Punch: They play something I like to call "tough guy" metal. They've written some remarkable guitar riffs.
Haggard: This band has 16 people or so playing a wide array of different instruments. Sounds a bit folkish, with heavy guitar riffs and awesome growling vocals.
Iron Maiden: Do I even need to say anything about them?
King Diamond: Most of the people I know that are into metal tend to avoid him. Everyone who play in his band is really good and his lyrics are fucking awesome. Really worth checking out.
Korplikaani: They play folk metal and kick ass while doing it.
Lapis Lazuli: Never listened anything from this Japanese band other than their Guilty Gear tribute CDs. The vocalist is really good, but suffers from the "generic japanese rock singer" disease.
Megadeth: I'm not fond of the pre and post Marty Friedman eras. It is a thrash metal band, but they have some really nice and melodic guitar riffs.
Necrophagist: Really fast paced Technical Death Metal band from Germany. Muhammed can shred while wearing a baseball cap backwards without losing his metal pose and I respect him immensely for that.
Onmyouza: A Japanese Power/Speed/Folk-ish Metal band. Their lyrics focus on japanese folklore.
Opeth: Fuck yeah! You are the coolest metal band ever! Opeth plays Death Metal with heavy influence from progressive rock.
Otyg: Andreas Hedlund's folk metal side-project, his songs in this band are written in a more traditional Scandinavian folk style, features instruments not frequent in your average metal band.
Ozzy Osbourne: He isn't even a good singer, but managed to gather the most impressive amount of really good musicians over almost 30 years of his solo career.
Pantera: I wasn't into more "extreme" genres of metal until I listened to Pantera for the first time.
Racer X: The band is kind of dorky, but it is still awesome. Like you could expect anything other than awesome coming from a Paul Gilbert's band.
Rainbow: That's what you get when you mix Ritchie Blackmore and Dio: Awesomeness. Or Rainbow.
Seikima-II: A band led by the former Vice-king of Hell. He, along with his band, managed to conquer the Earth with Heavy Metal.
The Old Sepultura: Because Sepultura's newest formation sounds nothing like the Old Sepultura.
Sex Machineguns: My favorite japanese Metal band. Their lyrics are really crazy and sometimes they make no fucking sense at all. Really awesome guitar solos and vocals.
Siam Shade: Looks like an average japanese rock band that focus on looking awkwardly gay (even tho they aren't "visual kei") at first sight, but if you listen to any of their albums, you'll be left in awe, their music is really awesome. Also suffers from the generic japanese singer disease.
Strapping Young Lad: Another band led by the most awesome candian to be born (after Rush), Devin Townsend.
Symphony X: One of the few Progressive Metal bands that sound REALLY good and don't bore me at all. The whole band is awesome.
Testament: In 1994 their label told them that if they didn't record a "mainstream" album, they'd be in deep shit. With that said, they recorded Low. One of the songs is based on the series of OVAs Chojin Densetsu Urotsukidoji. If you know those OVAs, you can guess what happened after that :P
Trivium: I know that they aren't really metal, but still, sound awesome.
Van Halen: I've been liking this band even before acknowledging what "metal" was.
X Japan: One of Japan's greatest metal band ever.
That ends my list. And my first post in this forum, hello everyone :P