ARIAS offers up about 1.5 million historical records, with more, hopefully, to come.  The records are all military files from various conflicts dating back to the Revolutionary War:

This is a decent collection, especially for historians, genealogists, and family history researchers looking for records of their family's military roots.  

Unfortunately, there is no global searching at ARIAS, so that each collection has to be accessed and searched individually.  The images of the actual records are not particularly good quality.  Hopefully, as Pennsylvania grows their archives, they will follow the lead of other states, and introduce a more robust search feature, and better imaging.