These blogs are great sources for original and thoughtful math activities.
Fawn Nguyen's blog
The Math Lab @ Room 27
Questioning My Metacognition
Steve Miller's Math Riddles
Dan Meyer's blog: dy/dan
Geoff Krall's blog: emergentmath
Would You Rather?
Don Stewards blog
Becoming the Math Teacher You Wish You'd Had
Robert Kaplinsky's Site
Mr. Orr is a Geek.com
Henri Piccioto's Math Education Blog
Essays about Secondary Standards