The Day of Defeat Source summer update was released last week, containing the new Detonation game type and the new maps: Jagd and Colmar. In a way of celebration, Valve is offering a free weekend of Day of Defeat gaming, commencing on Friday, July 7.
From July 7 at 1p.m. PST (5am GMT) all the way through to July 10 at 1pm PST (in case you've forgotten, that's 5am GMT), Day of Defeat Source will be made available to anyone fancying a game. If after the free gaming is over, you feel you can't possibly live a day longer with a DoD fix then you'll have to buy the game to continue playing.