Sherpa RoMEO maintains a list of Publisher Copyright Policies and Self-Archiving. Publishers are identified by colour, with white being the least author-self-archiving friendly (self-archiving not formally supported), and green being the most author-self-archiving-friendly (self-archiving of preprints and postprints is permitted).
As of today, even the Sherpa RoMEO white list is looking very green! This is because even a great many publishers with no overall policy supporting self-archiving, have green checks indicating compliance with funding agencies' open access mandates. Yet another sign of Transitioning to Open Access. As more publishers modify their policies to accomodate research funding grantees, watch for more and more movement towards full support for author self-archiving.