Penn Pilot is excellent. It is run by the state. They have a bigger collection of aerials at their aerial and topo library located north of Middletown. Another good site is Historical Aerials. Other states like Pennsylvania have aerial collections on line. Iowa is one that is real good. and Indiana is another.
Not all former tracks are buried under malls, houses and such. There are some good ones out there like Berwick Beach Haven, Rummage's Grove at Hunlock Creek, Greater Pittsburgh at Clinton, of course Circle M at Auburn. Some others include Bowling Green, Sportsman's, Fireball Stadium, Clearview near Aliquippa, Glen Drive, Hickory, the big Hustontown track, Iroquois, Lancaster, Langhorne (the back part of the track is still there), Sanatoga, Mount Joy, Motordome Ruffsdale, Mountain View, New Uniontown, Penn, North Hills, Queen, Spring Church, Three Point, Thunderbowl, West End, and more.