Suneo Hair - Waltz (OST Honey and Clover)
Nakagawa Shoko - Sorairo Days (OST Tengen Toppa Gurren Lagann)
Aoi Tada - Brave Song (OST Angel Beats)
Merengue - Bokira ni Tsuite (OST Ping Pong)
...basically, all songs by Kajiura Yuki, all songs in Angel Beats
There are many beautiful japanese songs