Andrew Ranicki - A wealth of mathematical articles and links
Mark Powell, Julia Collins, Spiros Adams-Florou, Chris Palmer, Carmen Rovi and Supreedee Dangskul.
Maths (other):
Will Merry - Excellent selection of notes for differential and complex geometry
Alexei Kovalev - "Skeleton notes" contain a good explanation of vector bundle connections (and much more)
The Manifold Atlas
Other:
Olly Moss - Designer extraordinaire
Capoeira Senzala - In my spare time
PHO - Some photography