Black Mesa: A Half-Life 2 modification
Normal Quality (double click on it to open the video on youtube and select High Quality for HQ)
Can't wait for it. The team did type when they released this trailer on 30 November 2008, that the days of development are numbered. So, early 2009 is my guess but mid-2009 is in a pessimistic ballpark for a figure.
Price of Mod: Free if you have any Source engine game.