TopCoder and CodeForces have competitions roughly every week and last 2 hrs long. You can also 'compete' (unranked, but will be timed) in old competitions on Co

TopCoder and CodeForces have competitions roughly every week and last 2 hrs long. You can also 'compete' (unranked, but will be timed) in old competitions on CodeForces or browse a huge laundry list of old problems. Most of the top competitors on these sites have either won ACM, USACO, IOI,etc. but there are lot of beginners and good tutorials.