Session Series (Drum Mania, Guitar Freaks & Keyboardmania)
The Least 100sec, and its long version The Least 333sec by Hirofumi Sasaki, from Guitar Freaks 5th Mix & Drum Mania 4th Mix. The latter in particular contains some beautiful piano playing, while still retaining the epic main part from the shorter version.
brave! by TERRA from ee'MALL 2nd Avenue. ee'MALL was a short-lived internet-link system capable of unlocking content for Konami arcade games. brave! appeared in pop'n music and Guitar Freaks+Drummania.
Pink Rose, originally from Keyboardmania, and has since appeared in pop'n music, DDR, and IIDX. The full version is an even bigger dose of the same kind of awesome.
The Day Dream series in its entirety, but especially Model DD7, from Guitar Freaks and Drum Mania V2.