I'm looking for a site or book or any other source of tiny programming tasks one can implement in preferred language. Would be great if examples are present too. And would be superb if there're people who may review my code. May be there's a wiki of such tasks. I've tried to google, but found nothing that suits my needs.
I want to improve my skills in programming using certain language but don't have specific task at hand. Any advice would be greatly appreciated.
Try sourceforge, there are many interesting projects and many of them are looking for volunteers.
There's a book called "Programming Pearls" by Jon Bentley which is definitely worth reading and trying out...
Chris Rathman is one of at least a few people I've seen who are working the exercises in Structure and Interpretation of Computer Programs in multiple languages. I'm currently still in the Scheme phase, but it seems like a neat exercise to me!
You can make an account on topcoder.com and review all the questions used in past competitions. You can review other people's answers, in addition to reading articles that present the solutions and reasoning behind them.
In addition to the facebook puzzles mention, ITA Software has some interesting hiring questions: http://www.itasoftware.com/careers/hiringpuzzles.html