According to the talk on EN World, and persuasive evidence posted by poster MerricB, WotC will announce the 4th edition of Dungeons & Dragons at GenCon tomorrow. It’s going to be interesting to see what they do with the game, and how it ties into the digital plans they have.
UPDATE: This seems to be the first substantial information about the new edition.
UPDATE II: More meaty information here!
UPDATE III: Word is getting around.