Does anybody know of a good library out there for developing for Facebook using the REST API in C#. I've been using the Facebook Developer Toolkit for some time now, but have more recently become annoyed at how key functionality is broken (even in the updated 3.1 beta). I looked into using the Facebook C# SDK, but this only appears to have a version for .NET 4.0.
Facebook C# SDK says
Note: If you are looking for the WP7, Silverlight, .Net 35 builds of this project you will need to download the latest source and run the Build/runbuild.cmd. These builds are currently not in our "supported" release, but they should work just as well.
Facebook# is pretty good, though I had to workaround a few things.
You might not want to use the REST API, though; they're deprecating it and bits of it may stop working...
Having worked extensively with the Facebook C# SDK I can confirm that there is a 3.5 build in the latest version, you just need to run the build scripts. There are also numerous discussions on how exactly to get it to build properly.
I have found through all my research that this SDK is the most rapidly updated and dependable SDK for .NET. If you have any problems using it then just drop a question on stackoverflow with the tag facebook-net-sdk
and I'd be happy to answer