See new UNIT_POWER_* constants:
SPELL_POWER_MANA = 0;
SPELL_POWER_RAGE = 1;
SPELL_POWER_FOCUS = 2;
SPELL_POWER_ENERGY = 3;
SPELL_POWER_COMBO_POINTS = 4;
SPELL_POWER_RUNES = 5;
SPELL_POWER_RUNIC_POWER = 6;
SPELL_POWER_SOUL_SHARDS = 7;
SPELL_POWER_LUNAR_POWER = 8;
SPELL_POWER_HOLY_POWER = 9;
SPELL_POWER_ALTERNATE_POWER = 10;
SPELL_POWER_MAELSTROM = 11;
SPELL_POWER_CHI = 12;
SPELL_POWER_INSANITY = 13;
SPELL_POWER_OBSOLETE = 14;
SPELL_POWER_OBSOLETE2 = 15;
SPELL_POWER_ARCANE_CHARGES = 16;
SPELL_POWER_FURY = 17;
SPELL_POWER_PAIN = 18;