RavenDB is a nice middle ground: eventual consistency for queries for speed, but ACID for create, update, and load (one or more items by ID).
It uses transactions throughout, so a failure in the midst of 10 writes will rollback all of them, as one would expect in a traditional relational database.
[0]: http://ravendb.net/
[1]: http://ravendb.net/docs/article-page/3.0/csharp/start/gettin...