One more .Net driver for connecting to MongoDB - NoRM - open-source library managed on GitHub.
Speciality of this project in linkage of .Net types and document model of MongoDB.
With NoRM very easy to manipulate with .Net type without necessity to copy them to/from documents for saving/resolving in/from DB like MongoDB-CSharp Driver.
NoRM Home http://wiki.github.com/atheken/NoRM/
Sample
var coll = (new Mongo(connString)).GetCollection<Product>();
//create a new object to be added to the collection
var obj = new Product();
obj._id = ObjectId.NewObjectID();
obj.Title = "Shoes";
//save the object
coll.Insert(obj);
//find the object
var obj2 = coll.FindOne(new { _id = obj._id}).First();