math blogs– list of online communities like blogs and wikis (“Online Resources”)
math institutions– links to main institutions and societies and to lists of more institutions
math archives– links to archives of writings and video lectures in areas of relevance to the $n$lab (including physics, philosophy)
math resources by individuals– links to math resource webpages of individuals in areas of importance to the $n$lab
Some other lists are:
Math on the Web – links maintained by American Mathematical Society
MathOnline is dedicated to collecting free mathematics resources, like books, lecture notes, videos and more. Using reviews, votes, and a tagging system, all this material is kept organized. (No DNS entry as of 2012-07-14.)
Wikipedia: Funding Sources for American Mathematicians
mathematics resources