Mathematics In General
- The CTRC category theory seminar in Montreal.
- MathOverflow and StackExchange.
- The DataGenetics blog.
Math Contest Related
- Paul Zeitz's Art and Craft of Problem Solving is at the perfect level for CEGEP students. It's written in an engaging, conversational style, and has nice problems at the end of every section. This is an amazing book.
- The Art of Problem Solving online community and textbooks are great.
- The CEMC at waterloo maintains a page of links to past contests.
- Old Putnam problems can be found at this page.
Math Curriculum Related
- Desmos is a beautifully designed graphing calculator webapp.
- Cornell has published a set of very nice conceptual calculus questions.
- Find the error is a short online set of interesting calculus problems.
- Gilbert Strang's fantastic linear algebra lectures from MIT.
- This silly calculus text is a good read for those already versed in the basics.