Programming contests:
https://code.google.com/codejam Google Code Jam
http://www.usaco.org/ USA Computing Olympiad (USACO)
http://cerberus.delos.com:790/usacogate USACO training gateway
http://icpc.baylor.edu/ ACM International Collegiate Programming Contest (ICPC)
http://uva.onlinejudge.org/ ICPC Universidad de Valladolid On-line Judge
http://projecteuler.net/problems Project Euler
http://www.hpcodewars.org/ HP CodeWars
http://community.topcoder.com/tco13/ TopCoder Open (2013)
http://community.topcoder.com/tc?module=Static&d1=hs&d2=home TopCoder High School (not since 2010)
http://www.codechef.com/ CodeChef - India's Largest Programming Competition
http://icfpcontest.org/ International Conference on Functional Programming Contest
http://www.acsl.org/ American Computer Science League
http://www.continentalmathematicsleague.com/ Continental Math League Contest
http://www.cs.sbu.edu/contest/ St. Bonaventure University High School Programming Contest
http://en.wikipedia.org/wiki/Competitive_programming Wikipedia: competitive programming
http://lmgtfy.com/?q=programming+competition+OR+contest Others...
Local greater-Boston contests:
Bristol Community College: March?
http://www.fitchburgstate.edu/academics/academic-departments/computer-science-dept/high-school-programming-contest/ Fitchburg State: December and May
Providence College: March
http://web.cs.wpi.edu/Resources/Contest/ WPI: March