"Popular modules that don't yet support Python 3 include Twisted (for networking and a bunch of other stuff), gevent (like Twisted but different), Django and Pylons (for building websites), py2exe (for packaging your application for Windows users), and PIL (for processing images)". (Pitrou)

Pitrou, Antoine. "Python2orPython3." Python Software Foundation Wiki Server. N.p., 9 Dec. 2011. Web. 14 Mar. 2012. <http://wiki.python.org/moin/Python2orPython3>.