Last October (I know this is "old" news, but my small group was discussing divorce yesterday), David Instone-Brewer and John Piper had a very informative debate on divorce. Instone-Brewer defends a position which would allow divorce for 1) adultery 2) persistent emotional and physical neglect and 3) abandonment and abuse.  Piper responds with a position that only allows for divorce in the case of "fornication during betrothal" .
Later, Andreas Köstenberger weighs-in and offers a position that would allow divorce for 1) adultery and 2) non-believer's abandonment of a believer.  In another blog post, Köstenberger answers questions in regards to his position, which is definitely worth reading 
Divorce is a tough topic and I sympathize with all the position mentioned above, but I think Köstenberger probably has the best interpretation as it relates to the plain biblical texts on divorce, but I am very intrigued by Instone-Brewer use of extra-biblical sources to hash out the meaning of Jesus and Paul.
 See Instone-Brewer's CT article, "What God Has Joined: What does the Bible really teach about divorce?" and his short response to Piper's critique.
 See Piper's article, critiquing Instone-Brewer, entitled "Tragically Widening the Grounds of Legitimate Divorce: A Response to Instone-Brewer's Article In Christianity Today".
 See Köstenberger's blog entry, "Clarfying the NT on Divorce"
 See Köstenberger;s blog entry, "Q&A on Divorce and Remarriage". *A MUST READ!!!!)