Resources

Competitions

Math

University of Waterloo math contests: http://cemc.uwaterloo.ca/contests/contests.html
Canadian Open Math Challenge (COMC): http://cms.math.ca/Competitions/COMC/
Canadian Mathematical Olympiad (CMO): http://cms.math.ca/Competitions/CMO/
American Mathematics Competition (AMC/AIME/USAMO): http://amc.maa.org/
Asian Pacific Mathematics Olympiad (APMO): http://www.mmjp.or.jp/competitions/APMO/
International Mathematical Olympiad (IMO): http://www.imo-official.org/

CompSci

Canadian Computing Competition (CCC): http://cemc.uwaterloo.ca/contests/computing.html
USA Computing Olympiad (USACO): http://www.usaco.org/
International Olympiad in Informatics (IOI): http://www.ioinformatics.org/index.shtml

Physics

University of Toronto POPTOR: http://www.physics.utoronto.ca/students/outreach/poptor
CAP Secondary School Prize Exam: http://www.cap.ca/
Canadian Physics Olympiad (CPO): http://outreach.phas.ubc.ca/CPO/english/
U.S. Physics Team: http://aapt.org/physicsteam
International Physics Olympiad (IPhO): http://ipho.phy.ntnu.edu.tw/

Biology

National Biology Competition: http://biocomp.utoronto.ca/about
Canadian Biology Olympiad (CBO): http://www.canadianbiologyolympiad.ca/index.html
International Biology Olympiad (IBO): http://www.ibo-info.org/

Chemistry

Canadian Chemistry Olympiad (CCO): http://www.cco-occ.ca/en/general.html
U.S. National Chemistry Olympiad (USNCO): http://portal.acs.org
International Chemistry Olympiad (IChO): http://www.icho.sk/