I work for WM-data Sweden, where I build large PythonPowered systems, mostly for meteorology (satellite and radar image production, all the way from the source to end-user products).
I used to work for the SecretLabs, also known as PythonWare. (And I still do some work for them, from time to time). At the SecretLabs, we do lots of PythonStuff, including PythonWorks, the PythonImagingLibrary, ElementTree, and more. We also work on TkInter and various part of the PythonInterpreter itself (including the RegularExpression library, UniCode, and XmlRpcLib).