Speaking of Western Pennsylvania, there are some useful books published by Sharon MacInnes, PhD. They are titled "Early Landowners of Pennsylvania: Atlas of Township Warrantee Maps of _______ County, PA". ( I have the Washington and Greene ones.) One nice thing is that you can get them with the actual maps on CD and so you can create your own cuts from them to show where your ancestors lived. They were printed by Closson Press. I know there are other counties available but I haven't checked to see if they're still in print or not. I expect they are, though. I'm not sure it the maps are available online or through the state archives. Anyway the value of the books is that they have indexes and transcripts of the information on the maps and notes from the old history books of the area.