I'd say if you are looking for a straight-forward way to integrate social site authentication, SocialAuth.NET is the way to go. It's API can communicate with other social sites such as Twitter, LinkedIn and Gmail.
Recently, I found a better and more efficient way to authenticate Facebook users on my site using Graph API and Hammock.
Hammock is a C# a REST library for .NET that greatly simplifies consuming and wrapping RESTful services. This allows us to embrace the social site’s core technology instead of using varied SDK's or API's. There are many community driven frameworks and API's readily available on the Internet, but they can really cause problems if they evolve too quickly or haven’t been thoroughly tested.
Suddenelfilio, has written a useful blog post on connecting Facebook using Hammock. You will see by his example that you can interact with Facebook anyway you want.
The same principle could also be applied to other website API's that use REST based services, such as Twitter.