this site is very good but depending on the area it might not go back very many years, in my area it normally goes back to the mid or early 40's but the overlay feature is priceless......... http://www.historicaerials.com/
http://alabamamaps.ua.edu/index.html is my favorite. If you look at the historic map index, not only do they have "regular" maps but in most cases, they have out of print quad maps for much of the United States.