There's a great deal of ongoing discussion about Agile Development and unit testing, since they are relatively new developments in the world of software. Online discussion groups are great places to learn more, get involved, and get advice about these technologies. A few of the thousands of active groups are listed here. Beyond these, it is not hard to find discussion groups dedicated to particular xUnits.
A Yahoo! group is dedicated to discussion of TDD and unit testing. Have a tricky unit testing problem? Want to listen in when unit test gurus discuss the finer points of the technology? Join this group. Find it at http://groups.yahoo.com/ group /testdrivendevelopment/.
A very active Yahoo! group dedicated to Extreme Programming. This is located at http://groups.yahoo.com/group/extremeprogramming/.
Another Yahoo! group, this one oriented towards refactoring and related topics. It is located at http://groups.yahoo.com/group/refactoring/.
Another Yahoo! Group, this one is centered on JUnit specifically . It is located at: http://groups.yahoo.com/group/junit/.