What standards cover foot prints for standard part packages?
It's the IPC-7351B - "Generic Requirements for Surface Mount Design and Land Pattern Standard"

The document only provides recommendations; there is no enforcement.  However, more and more manufacturers seem to be using it to inform their footprint suggestions.

Note that this spec isn't easy to use directly.  Instead of tables of land pattern dimensions, you see sections like this (take from a previous version of the spec):

....

Instead, I use a software called Library Expert.  It's free and quite useful. It creates footprints to the IPC-7351 spec.  It will actually build up the symbols for a number of software packages, e.g. Eagle, OrCAD, Altium, and others.