http://sprout.csie.org/oj --Test Online Judge
https://uva.onlinejudge.org --UVa Online Judge
http://poj.org --PKU JudgeOnline
https://code.google.com/codejam/past-contests --CodeJam
https://icpcarchive.ecs.baylor.edu --ICPC
https://www.codechef.com --CODECHEF
http://codeforces.com --CODEFORCES
http://acm.csie.org --NTU Online Judge
http://acm.hdu.edu.cn --HDU Online Judge
http://judge.u-aizu.ac.jp/onlinejudge --AIZU ONLINE JUDGE