It's funny to be writing this, considering that DotA 2 has been a permanent fixture in thousands of Steam accounts for well over a year now, but DotA 2 will officially launch later this year. It's currently in open beta, although people are selling their keys for less than ten cents in many cases, so its release status is cloudy at best.
Those of you that didn't want to buy, have no friends from whom to grab a code or just haven't been interested until now will be happy to know that DotA 2 will be available, free-to-play, in the Summer.