This site has code golfing challenges as well as other coding challenges. You can get reputation points for getting upvotes on challenges proposed or solutions submitted. Solutions are publicly submitted to the site. You can use any programming language as long as you have a way to run it online so people can test your solution.
Challenges limited to time frame (months) and are revealed at the end. Also has some restricted source challenges. People can add challenges subject to approval.
Weekly code golfing contests are held in the contests section from Sunday to Wednesday. Piston is used to verify solutions. Solutions are revealed at the end of the contest.
Here anyone can submit problems. Some go on forever with hidden solutions and others are timed contests where solutions are revealed after the time runs out.
Here you can compete in short Clash of Code challenges with others here or you can submit solutions on your own time here.
This is a JavaScript specific code golfing site. New problems are added occasionally. Problems go on indefinitely with hidden solutions.
Week.Golf
This site which hosted weekly golfing contests is no longer active, but an archive of solutions can be found on GitHub.