You'll find an updated list of .NET Twitter libraries on Twitter's developer site:
Twitter Developers: Twitter Libraries (for .NET)
- DotNetOpenAuth by Andrew Arnott – an OpenID, OAuth and InfoCard library
- Hammock by Daniel Crena – an HTTP API client supporting OAuth authentication.
- LINQ to Twitter by Joe Mayo – a LINQ provider for the Twitter API
- OAuth-Dot-Net by Chris – an OAuth library for clients and providers
- TweetSharp by Daniel Crenna & Jason Diller – a Twitter API library built with Hammock
- Twitterizer by DigitallyBorn – a Twitter API library (requires .NET > 3.5)
- TwitterVB by Duane Roelands – a VB.NET Twitter API library
