Which Mathematical Structure is Isomorphic to our Universe? - Max Tegmark. Some physical consequences of ``the ultimate ensemble theory'', where not only worlds corresponding to say different sets of initial data or different physical constants are considered equally real, but also worlds ruled by altogether dif - http://www.hep.upenn.edu/~max/toe.html
Mathematical Physics Archive - An archive of papers published in the field of mathematical physics. - http://rene.ma.utexas.edu/mp_arc/
Local Quantum Physics - Preprint archive with papers in PostScript format. - http://www.lqp.uni-goettingen.de/lqp/papers/