What area of physics do you want to know about? There are some free books (for example I know of one on small angle neutron scattering that you can find at NIS

What area of physics do you want to know about? There are some free books (for example I know of one on small angle neutron scattering that you can find at NIST)--also there are many lecture notes online. For texts, though do you think it would be better to have a static PDF, or a wiki, where an author could add what they could and the community could improve it?