There's a pretty good list here

http://wiki.python.org/moin/WebFrameworks

I'm sure the winners will depend on your needs. Do you need a full stack or not?

For me, it's either Django or Flask for Python depending on how much of a framework I want to start with. Both are mature projects in active development with a wide user base for assistance.

Right now I'm sort of in the Java world so Play! is my framework of choice.