Good friend of mine told me about interesting code competition provided by Google.
The website is here:
http://code.google.com/intl/cs/codejam/

Any free language is allowed for the competition, and it seems the tasks are always based on processing given input file and giving valid output.

Registration ends on September 3rd.

Qualification round gives you 24 hours, the following seem to be shorter.
The website has all the needed info.

Maybe it could be of interest for someone