Out of the few Twitter API libraries for .net out there, the ones that seem most complete are: Twitterizer and TweetSharp.
I’ve been developing with both in the past couple of weeks and both are generally stable, complete and provide a clean one-per-one wrapper for the Twitter API methods. Which is great news ™.
TweetSharp currently does not support the Streaming API, which is a major drawback and the reason why I am sticking with Twitterizer for now.
I recommend using the latest 2.3.1 source code of Twitterizer.
Small but important note: Twitterizer’s team is not currently officially supporting the Streaming API, so to use it (in assembly Twitterizer2.Streaming) – comment out the following line at the end of TwitterStream.StartStream:
Otherwise – it will not work.