No good options here.
I know, dabbrev does some neat things. But it pales in comparison to real code completion as you get in Visual Studio, or, I think, even SharpDevelop.
I checked out a module called csense that a lone developer hacked together last year. The goal of the project looked simple, focused, valuable: real code completion in Emacs for C# !!! Whoohoo!!!!! but
So the search continues. Real code completion looks to be pretty hard to get, and not easy to implement.
I think the next thing I may do is check out CSDE.
Jeez I hope I don't start considering implementing this meself. That would be a disaster. Somebody stop me.