The Furstenburg Conjecture and Rigidity - If two commuting endomorphisms of a torus are incommensurable (no power of one is a power of the other), then their joint action should be rigid. Some of the conjectures and open problems compiled by the AIM. - http://aimath.org/WWN/furstenburg/
Open Problems in Dynamical Systems - A collection of papers outlining unsolved problems maintained at Stony Brook. - http://www.math.sunysb.edu/dynamics/open.html