• ACM-ICPC Live Archive  (Here you will find hundreds of problems used in the ACM-ICPC Regionals and World Finals. You can submit your sources in a variety of languages, trying to solve any of the problems available in our database.)

• CodeShef  (An ICPC-style online judge (uses SPOJ for the backend, i.e. judging solutions). It is fairly new (started around March 2009), and only has a few hundred practice problems. They have monthly competitions (one longer contest lasting for a couple of weeks and a shorter contest of a few hours duration) with prizes (t-shirts and cash prizes). The problems in the monthly contests are usually of a very high quality.The site looks very good and is nicely designed. )

• Codeforces  (A website about programming contests. So far there is a weekly 2-hour contest with ACM/ICPC style problems. Users have their own blogs, and the main page shows blogs entries of several users. Also there is a rating system based on the contest performance. The aim is to have everything available in Russian and English.)

• FZU Online Judge  (This site has provide a chance to intensify you programming skill and fluency. Most of the problems here are chosen from the previous ACM/ICPC and other related contest. You can have fun during the practice.)

• Google Code Jam  (Here you can practise on problems from previous competitions. They allow you to code in whichever language you want, which is really nice. The interface is excellent compared to most similar sites. )

• Light OJ  (Over 300 problems, most are of good quality. The problems are categorized, and the site has its own compiler, chat room, articles etc. Users can arrange their own contests with their own problems. They can also view submitted codes of other users for problems that he/she has already got accepted. The online judge is more of an educational site and is really good for new problem solvers. )

• UVA toolkit  (Designed to help users solve problems from the UVa online judge. This is very useful if you want to practice solving problems related to dynamic programming (DP), graph theory, number theory, computational geometry, or any other topic.)