Spatial Extensions for SQL Server 2005 is an opensource and freely available product that adds OGC SFSQL capabilities to SQL Server 2005. Note this was not possible with SQL Server 2000 and below because of the grave limitations of those products. SQL Server 2005 supports .NET within the database. We haven't had a chance to try this product out, but for those who have made the SQL Server 2005 jump, it looks very promising.
We must also add that this product is in the process of implementing OpenGIS compliance.