In October 2009, DotA Developer 'IceFrog' announced a great news that he has been hired by Valve and leading a team there "to do some very exciting stuff that you guys will love". However, there was no further information revealed about it. Later, it was rumored that IceFrog is coming with Valve DotA Based Game like Heroes Of Newerth & League Of Legends. But now, this news seems to be true.
UPDATE: DotA 2 has been announced.
Jon St. John, The voice actor of popular game Duke Nukem series had a post on his Twitter page claiming that he has done voice acting for Valve's DotA.
This pretty much means that IceFrog is coming with a DotA based game with Valve's collaboration. A while ago, IceFrog mentioned in his Q&A Session #4 that "We'll be making an announcement soon". Also, John mentioned the same about PAX Expo 2010 which is happening on early September and amazingly, Valve is listed on PAX website as an exhibitor.
If this really happens all the DotA players who were attracted/ moved to other DotA clones will
probably revert back to Valve's DotA on large scale. Let's see if IceFrog updates further about this on his blog.
Update: Valve has filed DOTA Tradmark.
Keep your fingers crossed!