I can't narrow it down to one, sorry.
For heavy psychedelic music (which happens to be one of my favorite nebulous genres), the 00's were pretty fantastic:
Om's discography
Boris - Flood (honorable mentions: Feedbacker & Pink)
Dead Meadow's discography
Queens of The Stone Age-Songs For The Deaf
Isis - Oceanic (and their subsequent albums)
Ocean - Here Where Nothing Grows & Pantheon of the Lesser
Conifer - Crown Fire
Electric Wizard - Come My Fanatics & Dopethrone
Not to mention Sleep's Dopesmoker finally saw the light of day.
Oh, and Oxbow's The Narcotic Story was an absolute masterpiece.
Rap/hip-hop had a pretty good run of it too, with Aesop Rock's Labor Days, Fast Cars EP, and None Shall Pass all being A+.
Plus, Phish's newest studio album was great, and The Disco Biscuits had a bunch of awesome live records (The Wind at Four to Fly, the Trancefusion Radio series), so my Jam band fix got met and exceeded.
As far as electronic music:
All of the singles DMZ released, not to mention the genre (dubstep) didn't exist before Y2k
Venetian Snares had rossz csillag alatt született
Merzbow had a really strong run in the last decade, too.
That's just off the top of my head, but it looks like there was a bunch of really great music that got released in the last decade.
