Online AP practice

http://143.215.129.137/apExam/

Problets
http://www.problets.org/ 

Code Chef Online Programming
http://www.codechef.com/

JavaBat
http://www.javabat.com

Practice-It
http://webster.cs.washington.edu:8080/practiceit/

Project Euler
http://projecteuler.net/

UVA online judge (use FireFox)

http://uva.onlinejudge.org/

ICE Georgia Tech AP Practice
http://143.215.129.137/apExam/StudentLogin.jsp

http://143.215.129.137/apExam/TeacherLogin.jsp

Dwite
http://dwite.ca/