I have the 'luck' of develop and enhance a legacy python web application for almost 2 years. The major contribution I consider I made is the introduction of the use of unit test, nosestest, pychecker and CI server. Yes, that's right, there are still project out there that has no single unit test (To be fair, it has a few doctest, but are broken).
Nonetheless, progress is slow, because literally the coverage is limited by how many unit tests you can afford to write. 
From time to time embarrassing mistakes still occur, and it does not look good on management reports. (e.g. even pychecker cannot catch certain "missing attribute" situation, and the program just blows up in run time)
I just want to know if anyone has any suggestion about what additional thing I can do to improve the QA. The application uses WebWare 0.8.1, but I have expermentially ported it to cherrypy, so I can potentially take advantage of WSGI to conduct integration tests. 
Mixed language development and/or hiring an additional tester are also options I am thinking.
Nothing is too wild, as long as it works.
Few things help as much as testing.
These two quotes are really important.

"how many unit tests you can afford to write."
"From time to time embarrassing mistakes still occur,"

If mistakes occur, you haven't written enough tests.  If you're still having mistakes, then you can afford to write more unit tests.  It's that simple.  
Each embarrassing mistake is a direct result of not writing enough unit tests. 
Each management report that describes an embarrassing mistake should also describe what testing is required to prevent that mistake from ever happening again.  
A unit test is a permanent prevention of further problems.
Looking for testing/QA idea for Python Web Application Project