As others have already noted, aerial photos are useless in wooded 
terrain, which is a lot of what we face here in the northeastern US.  
Detailed topographic maps give you enough information to predict the 
most likely locations for historic (and prehistoric sites) if you can 
analyze the settlement patterns from already known sites.  For historic 
sites, there is also a lot of use of the detailed historic atlases of 
the late nineteenth century.  they didn't have topo lines, but streams 
and roads usually provide enough information to tie in with the current 
geography.
And in urban areas, of course, there are the wonderful Sanborn fire 
insurance maps, so detailed that they show sheds and outhouses, as well 
as the actually footprint of buildings.
The one time that I found aeiral photos useful was in looking at a 
farmstead that was included in a WPA aerial survey.  It gave me a chance 
to see what this rural site had developed into in the first half fo the 
20th century, but I was frustrated that it didn't have finer pixel 
resolution.
Meli Diamanti
Archaeological & Historical Consultants, Inc.