Bartlett Publishing has put together several lists of books available from many various publishers which are essential reading for anyone interested in the topic. Check them out today!
You can view the articles from the blogs which preceded these at the following URLs:
This post over at ETC shares a lot of my issues with the notion of a single "original text". Check it out! It's wierd that so little of this nature of multiple authorial texts is discussed in seminary. Even at a liberal seminary, the operating assumption is that there is a single "original text". If you imagine the process of handwriting each copy, its actually possible (though remote) that _all_ variants are actually part of some "original text".