A fantastic online research source has recently become available, thanks to the Arts & Humanities Research Council working in conjunction with the Universities of Reading and Southampton. It's called the Medieval Soldier Database and is an online listing of medieval soldiers that served in the English army between the late 14th to 15th century.
The original muster rolls have been transcribed, and it is possible to search under the following categories: first name; surname; status; military rank; captain name; commander; year; activity and reference.
The database is designed to act as part of a study into soldiers in late medieval England. It is also great fun and very user-friendly. I entered my family surname into the 'Search' section, hoping to find evidence of ancient Pillings tearing up the battlefields of Agincourt etc, but sadly nothing came up. It seems that my innate cowardice and complete lack of martial skill are hereditary!
Others may have more luck. Check out the link below and go play!