Mathematics: Miscellaneous Mathematics Resources

http://polymathprojects.org/ is a site that organizes mass collaborations to solve mathematical problems most amenable to that technique.

http://www.wolframalpha.com/ is a ubiquitous tool that can help with everything from looking up mathematical concepts through crunching through math problems.

http://www.birs.ca/ is a website for the Banff International Research Station for Mathematical Innovation and Discovery, which is sharing a large number of videos from workshops and conferences, as well as reports and conference proceedings.