One of my current favorites is Yuu Yamada's "Fly So High," from the Blue Dragon anime. I swear every time I hear it I want to get up and start dancing. XD
I also have a real soft spot for Inuyasha's "Sotsygyou: Sayonara wa Ashita no Tameni" and also "Four Seasons" and "Rakuen." ^^ I really *heart* Rakuen. I have a soft spot for most of the Inuyasha theme songs. ^^
Plus there's Hitomi Shimatani's "Falco," from Ueki no Housoku, which is actually partially responsible for getting me into the anime. Hitomi Shimatani is one of my favorite J-singers (one of the few I'll actually buy CDs for, rather than just a single or two), and I really loved the theme. Watched the anime and found out Kappei Yamaguchi was playing Hideyoshi and it was a done deal. *LOL*