- Interactive math miscellany and puzzles. Definitely the best.
- The rec.puzzles newsgroup has an archive and an FAQ page
which contain a wealth of information about many interesting problems.
- This is the FAQ page for the sci.math newsgroup which
is another place you can search for answers.
- Shack's math problems
- This is a similar page that contains
interesting math problems.
- This is the
Canadian site for International Mathematical Olympiad which is a
yearly competition for high school students.
- This is a course developed at Dartmouth aiming to make students more informed, critical readers of current news stories that use probability and statistics.
- This is a database of geometry problems.
- Heard on the Street
- This is a collection of questions asked in Wall Street job interviews.