Greg Martin (UBC)  
   Syllabus and practice problems from Rajiv Gupta and Greg Martin's Putnam practice sessions.
   http://www.math.ubc.ca/~gerg/teaching/putnam/

Madras College Mathematics Department Resources  
   Assortment of materials including British Mathematics Olympiad papers and Mathematics Higher Course Notes.
   http://www.users.zetnet.co.uk/madras/maths/resources.html

Problem Solving References & Resources  
   Overview of seminars oriented towards problem solving. Includes sample problem sets, list of online resources, college mathematics journals, and useful books. Maintained by Andrew Bernoff (Harvey Mudd College).
   http://www.math.hmc.edu/~ajb/PCMI/problem_solve.html

Ravi Vakil (Stanford)  
   Training resources for the Putnam competition. Practice problems, notes on mathematical theories, and recommended reading.
   http://math.stanford.edu/~vakil/putnam03/

Mathematics Olympiad Lecture Notes  
   By Greg Gamble for highschool students intending to participate in Mathematics Olympiads.
   http://www.maths.uwa.edu.au/~gregg/Olympiad/

Tutorials in Elementary Mathematics for Math Olympiad Students  
   Series of tutorials to cover the material of the unwritten syllabus of the IMO.
   http://matholymp.com/TUTORIALS/tutorials.html