I wouldn't say I'm a huge metalhead as I don't listen exclusively to metal and I don't really delve into sub-genres and the darker stuff. But I regularly listen to heavy metal and some trash metal. Metallica was the first band I got into, I had a huge Metallica phase when I was 15, that was pretty much everything I listened to for a whole year. The 200th time I heard the guitar in the chorus of Welcome Home (Sanitarium) I was as into it as the first time. I'm not as into them as I was but I still love them.
My favourite band of all time is Led Zeppelin, whether they are metal or not is debatable, probably not but they have influenced a massive part of the metal scene.
The metal bands I listen to regularly are Black Sabbath, Pantera, Down, Megadeth, Exodus... I guess thats it. I like Iron Maiden but I dont listen to them that much anymore.
I've seen Metallica (x3), Slayer, Motorhead, Maiden and Down live. I think thats it.
Bonus nugget, best albums:
Metallica - Ride The Lightning
Black Sabbath - Master Of Reality (Sabotage and Headless Cross right behind, the latter criminally underrated!)
Pantera - Vulgar Display Of Power
DOWN - NOLA
Megadeth - Rust In Peace, boring answer but their most complete record. Peace Sells... shines more but is more inconsistent
Iron Maiden - Brave New World
Exodus - Bounded By Blood