There are several now-well-known mathematics blogs that make for consistently interesting reading: Gower's Weblog , Tao's What's New , Kalai's Combinatorics and more and Richard Lipton's blog are leading examples.
In discrete mathematics, the pages maintained by the SIAM Discrete Mathematics Activity Group provide many useful links, as does Doug West's Home Page . In universal algebra and lattice theory, there is a page maintained by Keith Kearnes with links to conference listings and a bibliographic database.