I've been looking into this also lately. If you hven't seen these threads, there may be tidbits within that are helpful:
http://cs.trains.com/mrr/f/11/t/221045.aspx
http://cs.trains.com/mrr/f/11/t/218852.aspx
http://cs.trains.com/mrr/f/11/t/217998.aspx
http://cs.trains.com/mrr/f/88/t/221282.aspx
Hope that some of this is on target.
Paul
Modeling HO with a transition era UP bent
Most of the time you will have to start with your ownbackdrop sheet material such as masonite or other material fastened to your layout. After that, you can either paint your own, or buy paper type or photo printed backdrops that you can glue on to the backdrop material you have installed.
Backdrop Warehouse has the best ones but they also cost the most.
http://www.backdropwarehouse.com/indexbdwh.htm
Walthers has the Instant Horizons line that can be used.
And Scenic Express also has different backdrop scenes.
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
I think the biggest suppliers are http://backdropwarehouse.com and backdropjunction.com. I ordered mine from backdropwarehouse a few months ago. I am modeling the same area as you and wanted a long continuous backdrop, and they seemed to have the best options for me. I posted this pic not long ago but here it is again since it shows the backdrop very well. You can get this particular backdrop from 8' to 36' long without reversing any of the scene, and also specify the height and vertical scaling that you want. They also have other backdrops that would fit the region quite well.
If you do a Search the Community located on the right you will find some good discussion here on both backdrop suppliers and backdrop selection.
Huntington Junction - Freelance based on the B&O and C&O in coal country before the merger... doing it my way. Now working on phase 3. - Walt
For photos and more: http://www.wkhobbies.com/model-railroad/
Are ther any good places I can find HO scale backdrops. I model west virginia and the lower area in Pennsylvania near there so hills are must-have. Thanks