Have you looked at Desktop Central?
Or perhaps for your specific need, MSP Center Lite?
I do use their Desktop Central product at a few client sites and it seems to do a decent enough job for keeping the systems up to date. If they have some of the 3rd party products installed (Adobe, Java, etc.), it will also maintain those w/o any additional effort.
(They didn't have the MSP product at the time, else I might have went that route).