I can't help you with the regional airlines, but I can guess that it's mostly going to be the smaller carriers like United Express, American Eagle, etc. Make a quick scan of the arrivals at Reading on flightarrivals.com and see what you see
The only other airport that may be of some interest is ABE in Allentown (about a 45 minute drive on some of PA's finest roads). I know that PanAm flies into ABE. There is another field south of ABE that has warbirds and private stuff but I can't think of the name or tell you how to get there (useless eh?).
If you don't mind the drive, PHL is about two hours (maybe less) from Reading.