You can get the release candidate of SQL Server 2008 from Microsoft Download or through your MSDN subscription.
The released version is scheduled for third calendar quarter this year.
This release includes support for upgrading failover clusters from previous versions of SQL Server, as well as several bug fixes and minor improvements that we have made in response to the extensive customer feedback we’ve received from previous CTPs.
More than 250,000 customers and partners have downloaded the previous community technology preview (CTP) releases.
SQL Server 2008 delivers on the data platform vision in four areas: Mission Critical Platform, Dynamic Development, Beyond Relational, and Pervasive Insight.