Rethinking Tradition in Modern Islamic Thought by Daniel Brown One of the best books out there. Charts the history of hadith/sunna within Islam, with a focus on the debates surrounding their legitimacy. Summary here: https://pressthat.wordpress.com/2007/05/09/rethinking-tradition-in-modern-islamic-thought-by-daniel-brown/ Read book online here: https://www.scribd.com/document/116836545/Rethinking-Traditions-in-Modern-Islamic-Thought-Daniel-w-Brown Advertisements
Transmission and Collection of Hadith by Jonathan Brown https://ahadithstudies.files.wordpress.com/2010/11/brown-hadith-collection.pdf (right click, save as) Or here.
Western debates over reliability and authenticity of Prophetic traditions (Hadith) Jonathan Brown gives a summary:
Jonathan Brown gives a summary on the history and methods of Hadith criticism: http://www.scribd.com/doc/41077970/Summary-of-Hadith-Criticism
An Introduction to Hadith by John Burton Burton-Introduction-Hadith.pdf (right click, save as)