So here's my list:
- CodeChef - I already have some first-hand experience in this contest.
- IPSC - This is a low-budget but very interesting contest organized by one excellent team in Slovakia. It's open to everyone in the world, of course.
- Google Code Jam - I am currently exploring this contest. It looks promising.
- Facebook Hacker Cup - This is a bit messy. See below.
I hesitated to add Facebook Hacker Cup to the list. It has schedule where 2014 competition actually starts in 2013, which made me miss the competition. More importantly, Facebook insists on integrating the competition into Facebook website, which makes it really hard to access. You cannot even view the full scoreboard without logging into the website first. That's not very good when you want to use your ranking to look better in the eyes of your prospective employers, investors, or girlfriends.
I cannot recommend TopCoder Open, because of its association with NSA, hidden scoreboard (so girls don't know whom to chase), developer-unfriendly website (which is business-friendly, on the other hand), the omnipresent smell of money, trading of your private information, and the really awful java tool you have to use for everything from reading the problems to uploading your solution.
If you know of other interesting competitions, drop me a link in the comments.