Yes, Bart Ehrman's book on Lost Christianities is quite good in providing a history of early Christian diversity and how it died out and/or was stamped out. His companion book is Lost Scriptures, which provides his own translation of non-canonical early Christian writings.

The original work on this subject, though at the time much less developed than today, was Walter Bauer's classic Orthodoxy and Heresy in Earliest Christianity.

Other earlier translations of non-canonical early Christian writings include Wilhelm Schneemelcher's broadly inclusive New Testament Apocrypha and Robert Miller's more recent gospel-focused The Complete Gospels, which also includes commentary and comprehensive cross-references.

For other introductions to early non-canonical gospels, Helmut Koester's Ancient Christian Gospels is also excellent. J.R. Porter's The Lost Bible provides is a more visually elegant but still useful overview of non-canonical writings from both the Jewish pre-Christian days and from early Christianity. Elaine Pagel's Gnostic Gospels and Beyond Belief also provide histories of early Christian diversity.

It is important to recognize that all of the above works, including Ehrman's, have their own editorial perspectives shaped by their own conclusions. So it is always worthwhile to have two or more resources to explore any given topic to help provide balance.

The bottom line is that early Christianity was much more diverse than tradition has led us to believe, and Ehrman's and others' books on the subject provide us with a very healthy perspective by which to view today's Christian diversity

For further exploration of this topic, you can browse http://www.bibletexts.com/qa/qa119.htm#diversity.