At both http://albumpl.us and http://jaavuu.com we use webapp plus pytenjin: http://www.kuwata-lab.com/tenjin/pytenjin-users-guide.html

In addition, we have a small home-grown framework ("glue") that holds it together, but it's probably only about 100-200 lines of code. The advantage is that we know it and can maintain/add features easily.

But then again we don't really need a low end CMS, which is what many of these other frameworks try to provide.

We use django, but yes, google only officially support webapp and you may end up having to translate docs from appengine entities to django objects.

Btw, we use webapp with some sugar on top to make it sweeter:

    import app

    class Index(app.request):
      def get(self):
        self.show('index')

    app.run('/',Index)

No framework in the whole world can make coding in AppEngine that easy.