Links

Mathematical

Yimin Ge's Maths Blog
My mathematical blog where I occasionally post problems, results or just random thoughts which might not be worth a paper.
oemo.at
The (german) website of the Austrian Mathematical Olympiad.
Mathlinks
A fast growing and very active community on problem-solving, especially olympiad problems.
International Mathematical Olympiad
The official site of the IMO.
IMO Scores
A clear site containing all IMO results and various statistics on them.
IMO Compendium
A collection of various olympiad problems and related materials.
Cut The Knot
A great collection of various mathematical topics and articles.
Mathworld
A large encyclopedia of mathematics.
Mathematical Reflections
A journal on olympiad-level mathematics.
Project PEN
A problem journal in elementary number theory.
Die Wurzel
A german mathematics journal, especially for high school students.
Math4U
A nice german problem collection.