My top ten would have to be these.
1. Stereo Pony - Hitohira no Hanabira
2. Kakusei Heroism ~THE HERO WITHOUT A 'NAME'~
3. God knows (From Suzumiya Haruhi No Yuutsu)
4. The Pillows - Ride on Shooting Star (FLCL)
5. Genshiken - Opening - Manzo - My Pace, Daioh
6. Tommy heavenly6 - PaperMoon
7. Odoru Akachan Ningen (Ending to "Welcome to the NHK"

8. X-Japan - Tears
9. YMO - RYDEEN
10. Kumikyoku 'Lucky Star Douga'
But I also have a back-catalogue of "Asian Kung Fu Generation" and random singles and albums of "Ali Project", "X-Japan" and "Yui". Oh and "Melt Bannana" but there not my favourites.