The year 2000 I was in the navy (coastal artillery). On an island. I remember I got on a leave early in the spring, and the new Stratovarius CD had just been released. I already loved Visions, which came out in 1997 and while I didn't own Destiny yet, I knew the hit song SOS because it was played everywhere, so I thought why not - so I picked up Infinite. It had everything. A great Derek Riggs album cover, huge epics and many catchy songs and massive guitar solos. It became the soundtrack of our crew. My commanding officer walked in one time as well, noticed the CD and just asked "oh hell yeah, the new Stratovarius! Is that good?!"
The other big album during my service was, for some reason, Rainbow's Down to Earth.
I got off in June or July and quickly got a job. Somebody at work hyped Nightwish, and me being a veteran of the metal festival scene just told him they're not that special - a Stratovarius clone with a better looking lead singer. I had seen them many times, but saw nothing special. However, I was also a regular at our local public library. They had a great music section. I borrowed a ton of shit from there, and discovered many great bands, incl. Slayer, Saxon, Savatage, Judas Priest. I usually borrowed like 10-20 CDs and briefly listened through the less interesting ones (why not, free CDs), and one time I had the brand spanking new Nightwish CD Wishmaster on the pile. I put it on and BOOOM, just like that I understood what I had missed out on previously. When I actually paid attention, they blew me away. They blew all the other bands away. Summer of 2000 is when I became a fan. I had that CD for 2 weeks before I had to return it because it had reservations, and I picked up my own copy and I also bought Oceanborn.
Another new release I remember sampling (library) and liking in the summer of 2000 was Californication by the Chili Peppers, but there was something that made it wear out fast and I never picked up my own copy until at least a decade later. 22 years later I own 2 (two!) Chili Peppers CDs so I've become a casual fan.
2000 was also when I got a Metal-Is sampler with Blaze Bayley's Silicon Messiah (the song) and an interview with Iron Maiden. I am now a massive Blaze solo fan.
Brave New World was also obviously a big event that year. I remember downloading a crappy Real Audio sample of Wicker Man in advance. Internet was a little different back then.
Unrelated, but I picked up Stratovarius' Destiny the next year as a gift to my girlfriend (future ex-wife), just so I could have copy. Sneaky selfish.