LordKudzu wrote:
Rating Buster will break down stats that will affect other stats only. It will summarize how much health you will gain from +stam (and if you have a mod like EquipCompare it will show you the amount that changes between the two items) or will break down agility into +crit and +dodge and the like. It will not show you how much AP you will gain from +strength however.
I found it more useful on my mage than on my shaman (though that could be because my mage is 70 and my shaman 44). The Rating Buster page on WowAce is a terrific resource for determining how to customize it to your liking.
Best of luck.
Strength is really easy, just take the number of strength and multiply it by 2 and BAM, you have the amount of AP the item gives.