For the RESTful stuff, there's a big push by the WCF team (now with Glenn Block of MEF fame) to build an HTTP framework: http://wcf.codeplex.com/wikipage?title=WCF%20HTTP There's also a half dozen Sinatra clones. MVC is still a strong option and MVC3 is about to be released. Another popular OSS server framework is OpenRasta. For REST clients, check out Hammock (hammock.codeplex.com) and RestSharp.org (which is my project).

JSON is still a mess in .NET. System.Json should be the answer, but it's not everywhere (it's in Silverlight but not the desktop or phone frameworks). JSON.NET is still the best option. There are some other up and coming JSON libs as well.

Any other questions or areas of concern?