For what I'm interested in - Connecticut specifically - you can also go to the University of Connecticut (UCONN). They have aerial photos for different years for most places in Connecticut and most of them are available (as .tif or pdf files) through the UCONN Map & Geographic Information Center (MAGIC) website: http://magic.lib.uconn.edu/ . This link should bring you to a page where all the online Aerial Photograph collections are listed: http://magic.lib.uconn.edu/
For example, if you choose the 1934 aerials, if you click on Map Preview this will bring up a search box where you can search by address: http://magic.lib.uconn.edu/
For more about Connecticut's aerial photos go to http://www.ctstatelibrary.org/
But beware: it is SOOOOOO very easy to get "lost" back in time when visiting these sites and lose tons of modeling time. Ask me how I know. But it is really just so cool to take a virtual fly over of the countryside as it was 70 years ago. At least in Connecticut's case, you discover very quickly how few trees there were (it was still very agricultural back then). But even more interesting - and frightening until you realize what happened - is seeing the photos of railroad lines with two trains on the same track heading toward each other! Thankfully, that's just the result of two photos that were taken on separate days overlapping each other. But the first time I saw it, I was pretty shocked!
I hope you'll enjoy these resources and will get some good modeling information from them. And thanks again to RichS for reminding me of where to find them!