your answer is that you should try your self more!
But some goods:
the ACM site: http://icpc.baylor.edu
http://acm.uva.es/contest/
http://www.codeforces.com
http://code.google.com/codejam/
and also
http://www0.us.ioccc.org/index.html
http://www.mycplus.com/featured-articles/programming-contests-and-challenges/
solved Programming tests [closed]