More of an old school guy, but looking forward to checking out some of the recommendations for newer stuff. My personal top 10 (across all sub-genres):
1. Slayer - Early Slayer was the best live band I've ever seen. Show No Mercy was great, but the first time I heard Hell Awaits, it was on a metal radio show before the album was released. The hair on my arm stood up when I heard the opening (title) track. Just amazing. Luckily I got to see them many times in the 80s. Every show at L'Amours in NY was sold out and the energy from the crowd was something that I never experienced again. Not even the time I saw them at the Felt Forum when everyone ripped up the chairs and flung the seat cushions on stage in the infamous "seat cushion riot".
2. Metallica - I started out in the contracts dept for Atlantic/Elektra as a temp for a year. I have the last page of their contract signed by all the original members (RIP Cliff). The A&R guy had a crush on me and asked for me to hand deliver their checks every quarter. Nothing like bringing up million dollar checks. The one advantage for the guy having a crush on me was getting lots of Metallica stuff. I remember one time when I worked in the warehouse, my boss wouldn't let me go meet Metallica upstairs. I was so mad that I broke a window in the mailroom. I ended up going upstairs anyway to meet them. This was around the And Justice album.
3. Iron Maiden - The Number of the Beast tour was my first time seeing them. I would have loved to have seen them with Paul D.
4. Sabbath/Ozzy - What's there to say that hasn't been said already.
5. Overkill - My first underground show was Overkill in 85. Saw them many, many times. I guess I was an immature kid at the time because I would always drop stink bombs when they played "Rotten to the Core". I cracked myself up watching Bobby Blitz complain about the stink and it being "really rotten to the core up here". "Feel the Fire" album still sounds great today.
6. Exodus - Bonded by Blood is one of the best, if not the best, thrash album of all time. The first couple of albums after Paul were still decent, but I hit the eject button afterwards.
7. Obituary - oh my god. There was nothing like "Slowly We Rot" when it first came out. I flew down to Florida immediately to see them with Malevolent Creation and Cynic. Probably my funniest Obituary story was when I smoked on the tour bus with Sadus (the guys from Demolition Hammer spiked the pot with pcp without us knowing at the time) and I went on a crazy trip. After running around the parking lot, I ran through a side door that led to the stage. I stood on stage for like ten minutes completely tripping while Obituary played. They left me alone the whole time until a couple of friends recognized me and got me down. A few years ago I was on the 70,000 tons of metal cruise and I ran into the Sadus roadie that told me what Demolition Hammer had done to the pot. Obituary played on the cruise. On the last day of the cruise, I woke up and saw Trevor of Obituary sleeping in my female bunkmate's bed. Small world.
8. Sepultura - I was a fan of Morbid Visions and Schizophrenia. I remember interviewing them by phone before they released Beneath the Remains. They stayed with my friend for 3 weeks before they kicked off that tour. Lots of good stories from hanging out with them. The only English that Paulo knew at the time was "show me your teets" and he basically said that to almost every girl he ran into. We took them to Slipped Disc on Long Island for a record signing. We also took them to see bands rehearse. Lots of things during those 3 weeks before they would become huge and famous. The worst story was moving into my friend's house after Sepultura left and finding Max's diarrhea-stained Batman underoos under the bed. These guys weren't the cleanest to be honest. Hard to believe that these are the same guys that now charge $100 for a picture in meet and greets.
9. Death - I became friends with Chuck after I interviewed him. It was always great talking to him, but he was a complex character. I really loved those first few albums. A lot of fans got turned off by Death's more accessible sound starting with Spiritual Healing, but I think most appreciated it later as they/we got out of our heavier/more extreme metal period.
10. Gwar - Never got into their music, but I could appreciate their stage show. Definitely entertaining.