This site is "devoted to the science of mycology (the study of the fungi) and the hobby of mushrooming (the pursuit of mushrooms)" and it has an excellent page of links about mushrooms and mycology in general. There is a general emphasis at the site on California, but the links are universal.

Resources include two full-length books Mushrooms of California and Boletes of California, as well as a Systematics resource guide, a directory of Mushroom Clubs, articles on mushrooms, and events relating to them.