Math/Organizational
The Mathematical Subject Classification
The Erdös Number Project
The Mathematics Genealogy Project and Grapher
American Colleges and Universities
Math/Diversions
The Mathematical Quotations Server --
My personal favorites
Harvey Mudd Math Fun Facts
MAA Online Math Columns
Macalester Problem of the Week
Math/Humor
Brown Sharpie
xkcd
Komplexify
The Sarong Theorem Archive
TeachPi.org
Games/Community
Board Game Geek
Funagain
Board Games with Scott
GameStorm
Index of Card games
Games/Play
Blokus
Abalone
Set
Ticket to Ride at Days of Wonder
River Crossing at Clickmazes
Tipover at Puzzlebeast