Rumours that Valve is planning on doing more with ultra-popular Warcraft III mode Defense of the Ancients All-Stars - or DotA - feel a lot less rumour-like now. The Half-Life developer recently trademarked "DOTA" for future use.
The developer of Team Fortress, Left 4 Dead and Portal filed a trademark request with the US Patent and Trademark Office last week, protecting "DOTA" for "Computer game software," "Electronic game software" and "Video game software". (Incidentally, Valve also applied for a "Portal" trademark of the same nature.)
While that's not confirmation that it actually plans on publishing the Warcraft III modification under its own name - Valve has plenty of trademarks that were never used for its games - the company's recent hiring of DotA Allstars developer "IceFrog" shows they have genuine interest in the game. Or at least the design skills behind the game.