buy luminary gold, luminary gold, cheap luminary gold, Shadow priest in a 25 player raid

Paladins – High Demand – Blessings, Auras, Bubbles, mana regen, can tank, heal, or DPS, what more could you want! Usually 3 are enough though to get all the buffs.
Druid – High Demand – Mark of the Wild, Innervate, Combat Rez, Cyclone, Root, bonus crit, and a ton of other abilities, combined on a class that can tank, DPS or heal. This is a solid class that most raids like having 2 or 3 of around if at all possible.
Priests – High Demand – Fortitude, Spirit, magic debuff, and health regen all combine to make this a high demand class where you want at least a healing and a shadow priest in a 25 player raid.
Shamans – Medium – Shamans can fill many cheap luminary gold, they can heal, melee DPS, and caster DPS. In addition they can self rez and have totems for buffs. Many fights go much easier with one around due to their tremor and poison totems, and many DPS go nuts if you do not have one, because they lose buffs. A great class to have 2 of in a raid, past that, It is not worth the spot.
Warriors – Medium – They can tank or DPS but lack huge group benefits past having 1 or 2 in a group.