Microsoft has released SQL Server 2008 officially, according to this press release.  The software is currently available to MSDN and TechNet subscribers:

SQL Server 2008 is now available to MSDN and TechNet subscribers and will be available for evaluation download on Aug. 7, 2008. SQL Server 2008 Express and SQL Server Compact editions are available for free download today at http://www.microsoft.com/sqlserver. As previously announced, pricing for SQL Server will not increase with SQL Server 2008. More information is available at http://www.microsoft.com/presspass/presskits/sqlserver.

Read the full press release for more details, or hop out to MSDN and begin downloading now before everyone else does!  Oh, and check out the new UI for the MSDN subscription center, too - the filter is awesome!