Here is list of some important mathematics blogs, magazines and other websites.
What’s new (Prof. Terence Tao, Fields Medalist)
Gower’s Weblog (Prof. Timothy W. Gowers, Fields Medalist)
Alex Bellos’s Adventures in Numberland (Alex Bellos)
Division by Zero (Dave Richeson)
Geometry and the imagination (Danny Calegari, California Institute of Technology)