Protection from Evil/Magic Circle vs. Evil to protect against their charm, suggestion, and dominate effects is a must. At higher levels, Mind Blank completely screws them over.
Against the mind blast, spread out, and put high-Will save people in key places. Summoned/created undead, constructs, plants, oozes, and vermin help a lot too, due to their immunity to mind-affecting abilities. Summoned elementals also work, due to their stun immunity.
Against their levitation, Mass Fly, Fly, and potions of flight help your melee types close with them.
Dimensional anchor will keep them from using their planeshift ability(though if they do, you've pretty much defeated them anyways).