Rigorous trivialities
n-category cafe
Noncommutative geometry
Number theory research
Neverendingbooks
Abstract nonsense
Arcadian functor
F_un mathematics
Theoretical atlas
Low-dimensional topology
Secret blogging seminar
Gowers, Tao, vivatsgasse
Not even wrong (Physics)
Kowalski
Mathematics and Physics (Borcherds)
Young mathematicians network
Slashdot
http://www.eurekajournalwatch.org/index.php/Main_Page
ResarchGate?
nLab page on Blogs