Over at the physics forums s3nnOc has noted two interesting new papers. One is a nice primer on M-Theory (that's the mod name for string theory, for all of you who are behind the curve), and another assessing the state of the Loop Quantum Gravity research program (i.e. look at a discrete or quasi-discrete time space as a way to reproduce general relativity from the ground up with simple rules).
Both papers call for upper level undergraduate or better backgrounds in physics and mathematics, and neither breaks any particularly new ground. But, both are good introductions for sophisticated readers unfamiliar with these fields.