Are there any particular libraries blocking you? Numpy / SciPy, IPython, Requests, Django, Pyramid, Bottle, etc. have all been ported to Python 3.
PIL as well. similar reasons. django image fields are dependent on PIL.
Celery is still on Python 2 also, and while there are other message queues available, none of them is as easy to integrate with for an app that's already written in Python.