A group for proposing problems, sharing ideas, discussing areas of research and reviewing papers and books of interest. [Requires Yahoo! membership] groups.yahoo.com/group/Erdos
Mathematics is useless on its own, it only has a function when used with something else (i.e. a toothbrush). An online discussion. www.mathsistoothpaste.org
Topica email list serving the users of the IRC channel #math on the Undernet, for discussion and challenging puzzles. lists.topica.com/lists/undernet-math