SomeGuyNamedKy said:
The Fooly Cooly soundtrack.
the pillows are the greatest J-Rock band imo.
Seconded.
I've always been partial to Lilium, the opening from Elfen Lied, but that just might be my apparent Latin fetish talking.
Other than that, I am absolutely in love with the openings from Sayonara Zetsubou Sensei, as Kenji Ootsuki is perhaps the greatest Japanese rock/metal musician to ever live, and I've always been rather fond of the majority of the music from Higurashi No Naku Koro Ni. Prime example being the first opening, as I've never heard anything that would have been quite so fitting for the insanity about to ensue in my life.
Oh, and I have massive amounts of respect for the opening of Speed Grapher. Bet you never expected an anime series to license Duran Duran's Girls on Film. I certainly didn't.