I'm proud to announce the first release of NHibernate.Spatial. This extension allows you to handle data in a spatial database using .NET objects and HQL queries in a way compliant with Open Geospatial Consortium specifications. Currently we support PostgreSQL (using PostGIS extension), SQL Server 2005 (using MsSqlSpatial extension) and SQL Server 2008 (using their new spatial built-in capabilities). More on features, setup and usage in our wiki site.
Download and enjoy!
UPDATE: Prefer the lastest release.