Mage Stat Priority(updated for 5.0.4)

The stats that your mage should be focusing on varies depending on what tree you are spec'd into. Below I have listed the stats you will want to focus on to maximize your dps. Please note the stats you will want to focus on can change depending on the level of your gear and your mage talent build, it is recomended that you use Rawr or SimC to maximize your DPS.

Mage Stat Priority:

Arcane Mage Stat Priorities:

1 Intellect Intellect is the best stat. Intellect increases Spell Power, Critical Strike Chance and Mana.
2 Hit Hit is a very strong stat, but still weaker than intellect. You'll need 15% hit.
3 Mastery Mastery is considerably weaker than Crit, now this could change if they want to increase the worth of mastery in future patches.
4 Spell Power Spell Power is a very strong stat.
5 Haste The Haste "Soft Cap" is +12.5% and you should try to get this point for raids, note that you can get this point some with buffs that are cast on you. After the Soft Cap, Haste is considered the weakest stat so don't have more haste than you need. This may have changed some in MoP so I will update this if needed when I know more.
Living Bomb, Pyroblast (Dot) and Frostfire Bolt (DOT) all gain an additional tick at +12.5% Haste.
6 Crit Crit is a very strong stat as the Fire spec is built around Crit: Hot Streak relies on crits.

 

Fire Mage Stat Priorities:

1 Intellect Intellect is the best stat. Intellect increases Spell Power, Critical Strike Chance and Mana.
2 Hit Hit is a very strong stat, but still weaker than intellect. You'll need 15% hit.
3 Crit Crit is a very strong stat for fire mages as it increases the free Pyroblasts you will receive.
4 Spell Power Spell Power is a very strong stat.
5 Haste The Haste "Soft Cap" is +12.5% and you should try to get this point for raids, note that you can get this point some with buffs that are cast on you. After the Soft Cap, Haste is considered the weakest stat so don't have more haste than you need. This may have changed some in MoP so I will update this if needed when I know more.
Living Bomb, Pyroblast (Dot) and Frostfire Bolt (DOT) all gain an additional tick at +12.5% Haste.
6 Mastery Mastery is considerably weaker than Crit, now this could change if they want to increase the worth of mastery in future patches.

 

Frost Mage Stat Priorities:

1 Intellect Intellect is the best stat. Intellect increases Spell Power, Critical Strike Chance and Mana.
2 Hit Hit is a very strong stat, but still weaker than intellect. You'll need 15% hit.
3 Spell Power Spell Power is a very strong stat.
4 Haste The Haste "Soft Cap" is +12.5% and you should try to get this point for raids, note that you can get this point some with buffs that are cast on you. After the Soft Cap, Haste is considered the weakest stat so don't have more haste than you need. This may have changed some in MoP so I will update this if needed when I know more.
Living Bomb, Pyroblast (Dot) and Frostfire Bolt (DOT) all gain an additional tick at +12.5% Haste.
5 Crit Crit is a very strong stat as the Fire spec is built around Crit: Hot Streak relies on crits.
6 Mastery Mastery is considerably weaker than Crit, now this could change if they want to increase the worth of mastery in future patches.

 

*Please note I expect these may change a bit after the expansion has been released to balance things.