Oh, I'm going to cite Yoko Kanno, do not doubt, but it won't be my first pick and it's not going to be either soundtrack you're thinking of right now.
Here's my top 5:
soundtracks: Not only are there the three soundtracks (for the Animation, the Natural, and the Origination seasons) there are also two piano-only collections (labeled Stagione and Dipartenza) which are also benissimo. Now, I'm not saying these CDs are for sale on English-language sites (even online) Which Is A Freakin' Tragedy And Can We Fix That? but I'm sure you can find these somewhere. It's light acoustic--definitely Italian-inspired--music, but I also relies heavily on both a European Cafe sensibility (think Paris, Prague, Barcelona, not just Venice) and while the guitar is wonderful, particularly when paired with both violin and accordion, those two piano CDs are just amazing -- and each of the seiyuu also acquits themselves quite well on the vocal tracks, managing to be both in fine voice and in character.
2. Read or Die
soundtracks. Both the OAV and the TV series produced excellent soundtracks, though if I had to pick a favorite, I'd go with the TV show main theme. It's all synth, though -- and while certainly not bad -- I wish they had money in the budget for a full orchestra on some of those cuts.
. Yeah, yeah, I know
. The music in the show is repetitious and that damn-music-box-from-hell-mixed-electronically main theme will haunt your dreams for weeks after you marathon the whole series -- but the mix of choral works, light incidental music, and the more dramatic themes hit me in the right way, and the 4 CD soundtracks are (or at least were) available from places like Rightstuf.
4. Brain Powerd
. Sure, you've heard Yoko Kanno take the whole oeuvre
of Blues, Jazz, and Funk (with a side of rock) and distill it into one great soundtrack (and if 15 other people don't mention Cowboy Beebop in this thread something is broken with fandom) but did you know she has done the same with classical? While many will have heard (and loved) her work on both Escaflowne and Gundam -- Brain Powerd is her unknown and under-appreciated masterpiece. You'll listen to the tracks and swear
you can think of the classical composer who wrote it, or which movie soundtrack (by Williams, say) that you've already heard it in, but no: It's just Kanno-sensei working undeserved magic for what is now a ten-year old generic dystopia/mecha show.
5. Najica Blitz Tactics
. In many ways this is just a rip-off of Bebop. "Oh, the kids like jazz now? OK, bring it." And not only did they copy the jazzy style, they even went so far as to form a house band (a la the Seatbelts) known as "Diligent Circle of Ekoda" and they requite themselves well -- sure, this isn't Bebop, or Kanno's later works (like GitS SAC or Darker Than Black) or even the Baccano soundtrack, which if you're not listening to you also need to seek out -- but since most of you know both Bebop and Baccano, I thought I'd point you to something similar, but different, and also pretty damn good when considered on its own merits.
Did you know there is a 10 CD box set
that was released, complete with dance remixes? This is so obscure, and of such little interest to anyone other than John and I, but I thought I'd throw that out there.