distance vector databases and country maps

I am looking for info on free/open source (or if that's not available,
any other product) products which can be integrated with PostgreSQL that
provide geometric vector data on geographic maps.

In particular, I need that for Germany. What I want to do is to find
cities within a 50-100 km radius of any given location on the map. I
know that quite a few people are working on this and that such solutions
exist; I just don't know where to start looking. Also, my impression is
that all of these solutions are heavily copyrighted, patented etc. and
that it's probably really expensive to get to use this kind of data.

Can anyone help out with info, starting points?

Thanks, Frank