This blog post is in response to several inquiry about Free Download of SQL Server 2008 R2 RTM.
Microsoft has announced SQL Server 2008 R2 as RTM (Release To Manufacture). Microsoft® SQL Server® 2008 R2 Express is a powerful and reliable data management system that delivers a rich set of features, data protection, and performance for embedded applications, lightweight Web Sites and applications, and local data stores.
Download SQL Server 2008 R2 Books Online.
Reference : Pinal Dave (http://blog.SQLAuthority.com)