I'm not a fan of remixes, but these really got my attention:
kanariya "Jonathan "Peters' Vocal Club Mix" (specially the pv version)
monochrome "D-Z WHITE INSTINCT Mix"
M "Above & Beyond Mix"
Free & Easy "Huge Heavenly Mix"
alterna × FREEFORM FIVE
HEAVEN × DAISHI DANCE
CAROLS × PLAYGROUP
And, do orchestra/acoustic versions count as remixes? If so:
ever free from ayu-mi-x III
HEAVEN "piano version"