Calyptus Lob provides Large Object (BLOB/CLOB/...) support for DDD ORMs on the .NET/Mono platforms. Such as NHibernate.
Pull request Compare This branch is even with sebmarkbage:master.
Latest commit 68cc4ac Dec 28, 2011 @sebmarkbage sebmarkbage Added support for Amazon S3 for external storage
You can also use S3Connection to another S3 bucket to retrieve S3Blob objects. These can be used as any other Blob object but can also be saved to your NHibernate mapped S3 store more efficiently than reading it and then writing it.