My recently published Six Revision guest post, 10 Puzzle Websites to Sharpen Your Programming Skills, got a great response, hitting the front page of Hacker News, Reddit, and doing fairly well on Digg too.
Lots of comments were left pointing out some sites which weren't included in my list, so I'm following up here with a list of 10 more top programming puzzle websites:
Code Chef has lots of practice puzzles, and monthly competitions with cash prizes. The site officially supports over 35 programming languages!
The Sphere Online Judge contains 1871 different programming problems. More points are awarded for better performing solutions, which can be submitted in a range of languages.
The aim with code golf is to submit a solution using the fewest characters possible.Solutions can be submitted in Perl, Python PHP or Ruby.
Over 2600 great programming puzzles, and also regular contests. Submissions in C, C++, Java or Pascal are automatically checked for you.
An online competition site that automatically checks your submissions. Supports Java, C#, Pascal, C and C++.
The code jam is a programming contest from Google. The top 25 contestants get to travel to Google's HQ in California. Entries are accepting in any programming language.
Programming puzzles designed to provide "pre-college students with opportunities to sharpen their computer programming skills". The puzzles are still interesting and fun even if you've got a CS degree!
A British version of the computing olympiad. Again aimed at school and college students, but fun and interesting for everyone.
About.com's C/C++/C# section regularly posts interesting programming puzzles. Successful solutions get acknowledged on the site once the deadline has passed.
A site dedicated to practical Java programming problems. You can type your code directly into the website, and it'll tell you if you've solve the problem correctly or not.