I can't find something like a specific map for itemdrops but logic dictates that the items work similiar to the way the difficulties work. Meaning that normal is designed for characters from 1-30, nightmare from 31-50, hell from 51-60 and inferno lvl 60 (a higher rate of equipment including sets).
The items that drop for me are normally 1-3 levels under my current level but lets just assume that a level 15 character going the standard way through normal can get lvl 15 drops around the time he grinds in his area. That would also mean that you can pretty much assume that act 1 has the highest range of items because its long and you level up very fast in the beginning. So my guess would be that itemdrops in act 1 are around 1-15 and following that logic in the other acts and difficulties.
I know it's a lot of guesswork but this is as close as it gets unless blizzard pusblishes a real map of the itemlevels.