very surprised noone has mentioned
www.gamespot.com which is responsible for the coverage of all the main gaming events in america including PAX, CES, E3, Nintendo World Summit, X10, Captivate and Gamescon just to name a few. You'll be able to find footage of stage demos for new and upcoming games, interviews with the developers including developers diaries for some games. There always up to date by the minute but I would suggest cross referencing interesting searches with youtube, never trully know if anythings that good unless you've seen or heard it for yourself!