Wizards of the Coast have announced in a press note that the fourth edition of D&D will be ready for may 2008.
The new features are integration with the plastic miniatures, web-based tools (including a "digital game table" to play over internet), faster gameplay and less gaming sessions preparation time.
For more details, read the press release.
The Hypertext d20 SRD is a fantastic website about the D20 system.
I've just added the link to the Links section, don't miss it if you play AD&D!