Just like the title says.
What I'm doing here is to match each of the Mane Six and other important ponies with appropriate class combinations.
Twilight Sparkle: Erudite(Psionic) w/ Spike as a variant Psicrysmal, or Wizard(Arcane) with Spike as a familiar/cohort (CPsi, or SRD)
Rainbow Dash: Scout (CAdv)
Pinkie Pie, Variant 1: Paladin of Freedom/ Bard Gestalt, except manifesting abilities as equal level Divine Mind, Freedom, Chaos, Knowledge mantles. (UA, CPsi)
Pinkie Pie, Variant 2: Bard / Psion(Nomad) (PHB I, XPH)
Rarity: Psion(Kineticist) 1 / Rogue / Master of the Unseen Hand (PHB I, XPH, CWar) or Psionic Artificer (ECS)
Applejack: Ra