I think it was Huxley that said that an intellectual is just somebody for whom sex is not the most important thing.
I'll mutate the meme beyond all recognizance. Having read one such work and re-read another recently, I'll just list a few books which inform or have influenced my thought on Christian origins in some significant way.
- Antiqua Mater by Edwin Johnson
Written in 1887, just three years after the publication of the recently-discovered Didache, this is an honest and well-argued skeptical examination of the early Christian literature, one that would greatly influence what would eventually develop into the mythicist position. I like his analysis of the Didache in contrast to Justin of Neapolis, especially in light of the fact that the Didache was a brand new text back when this volume was published.
- The Birth of Christianity by Joel Carmichael
Warning—This book is written in a way that requires the average reader to keep a hefty dictionary nearby. Nearly every sentence is a beautifully convoluted flurry of dexterous polysyllabic insight. If you can navigate the advanced lexicon used throughout, this book contains what I think is one of the best laid-out overviews of Christian origins that I have ever read in a single volume.
- The Origin of the New Testament by Alfred Loisy
Reading this 1930's work by this lovely apostate about ten years ago brought me for the first time face-to-face with the fact that any appeal to "apostolic" authority is tenuous at best.
- Orthodoxy and Heresy in Earliest Christianity by Walter Bauer
Another milestone work that forever changed the way I looked at the relevant materials. I've actually read this book in its entirety thrice. (OMG, I'm such a geek!)
- The Cross That Spoke by John Dominic Crossan
Though I have seen critiques of Crossan which dismiss him as an ultra-liberal fringe writer, and though this book in particular (and also his Who killed Jesus, which essentially demolishes Raymond Brown's multiple-volume treatise on the death of Jesus in a mere 100 pages) argues what might be seen as an especially fringe position on the original provenance of the Passion Narrative, I have never heard a single scholar try to refute it. Not one.
- Lost Christianities by Bart Ehrman
Although I think Ehrman makes a huge mistake in thinking that the catalyst of the movement was a historical Jesus who was an end-times monger (an error which pervades all of his subsequent theses derived from that one), his insights regarding the first and second-century variations are nevertheless fascinating and useful.
- The Incredible Shrinking Son of Man by Robert M. Price
This book helped me see that there is nothing new under the sun—not even the "New" Testament.