CodeKata is a blog of programming puzzles written by Dave Thomas, who’s most famous for the groundbreaking book, Pragmatic Programmer. The puzzles involve many issues that are directly relevant to real world programming so this is a good place to brush up on your coding skills.
Facebook has a collection of very challenging programming puzzles that–should you manage to solve them–could result in you getting a job at Facebook! Solutions are accepted in a variety of languages including Erlang, PHP, Perl, Python and Ruby.
Python Challenge features riddles that ask you to write small Python programs to solve. The difficulty level gets progressively harder and more cryptic. This is an excellent site for programmers/developers that like problem solving!
Quoted from their front page: “Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve ” The puzzles featured on the site range from relatively trivial to seriously complex!
Al Zimmermann’s self-described “arena where demented computer programmers compete for glory and for some cool prizes” is a great way to participate in the programming community. Contests run every six months.
Mind Cipher wasn’t included in the top 10 because this site doesn’t require you to do any programming. It does, however, include the “world’s greatest brain teasers, logical puzzles and mental challenges”, so if you’re just out for a quick mental workout this is the place to go!
99 Prolog Problems is suited to the Prolog programming language but people have provided solutions in Python, Ruby, Haskell, Scala and others. Working your way through these problems is a wonderful way to pick up a new language.