Here are a few general mathematical web sites
The Mathematical Genealogy Project - the academic pedigree of many mathematicians.
Erdös Number Project - information on collaboration between mathematiciaans.
UK maths department web sites - links to home pages of UK maths departments by Heriot-Watt University.
World maths department web sites - links to home pages of maths departments across the world by Penn State University.
Mathematical and scientific walk around St Andrews - a walk visiting interesting sites in St Andrews.
Ten Lessons I Wish I Had Been Taught - Gian-Carlo Rota's advice to young mathematicians, from the AMS Notices.