SQL Server 2012 (codename “Denali”) is the name for the next version of SQL Server. The CTP1 of Denali was released on Nov 8, 2010, and you can download it here. The next CTP will be available this summer, and you can signup to be notified when it is released (UPDATE: CTP3 made available here on July 12th, 2011).
UPDATE on 10/13/2011: The official name is SQL Server 2012.
I have other blogs that cover the following major new items in Denali: the new SSAS features, the new SQL Server Developer Tools, codename “Juneau”, and the new reporting tool called Project Crescent. Here are the best resources I have found that describe other new features:
What’s New (Microsoft help)
Microsoft SQL Server Code-Named “Denali” AlwaysOn Series,Part 1: Introducing the Next Generation High Availability Solution
The T-SQL Cookbook: What’s Cool in Microsoft SQL Server 2008 R2 and New in SQL Server Code-Named “Denali”