Richard Hosino is a local mathematician, professor, and novelist. We highly recommend reading his book, The Math Olympian

James Tanton is a brilliant mathematician and math educator. We use some of his resources for our Math Circles program. His website: http://www.jamestanton.com/

Math Pickle website is a great resource created by a mathematician/math educator named Gordon Hamilton. We use some of his materials at Math Circles and he has even been a special guest in our classes in the past! You can sort through his materials by grade or topic: http://mathpickle.com/

For practice on math competitions, we recommend doing the past Waterloo math contests: http://cemc.uwaterloo.ca/contests/past_contests.html

Videos:

Mathematics Olympian gold medalist talks about the art of math