Links

Math Links:
Math Overflow - great place to ask and answer (research level) math questions
StackExchange - great place to ask and answer (any level) math questions
nLab - wiki-lab for higher category theory
ALGTOP-L - algebraic topology list
arXiv - open access e-prints

Useful Stuff:
Bibtex - bibliographies in latex
xy-pic - diagrams in latex