I currently have a TCP server application written in .Net that receives and submits messages to clients. I am looking at building a web application so need the communication
I've used both technologies and work on both sides of the .NET / node stacks.
Update - removed jquery info since it is no longer applicable
Developing a scalable / thread safe TCP server may not be an easy task. On the other hand, there are very nice resources on the internet in order to start your own. For example, if you are just looking for some nice open source WebSocket projects, my advice would be ;
Alchemy Project : Open Source C# WebSocket Library
Fleck Project : Open Source C# WebSocket Library
SignalR could be nice but it needs Windows Server 8 / IIS 8 in order to provide WebSocket feature.
On the commercial product side, especially considering the websocket feature is not available on all the browsers, i recommend PokeIn WebSocket and reverse Ajax Library. Starting from version 2.0 it has built-in WebSocket server. Details available from here
SignalR is like Socket.IO in that it supports transport negotiation/fallback. It is a framework and not a server, so you need to host it on a server of some sort. We have hosts for ASP.NET, OWIN (e.g. Kayak) and self-host, so you can run it in your own process easily, e.g. a Windows service.
SignalR has supported clients for browsers (JS), .NET, Windows Phone 7 and Silverlight. There are also contributed clients for things like iOS, Mono Touch, etc.
SignalR will give you a much higher level API than raw sockets which is its big advantage, allowing you to do things like "RPC" from server to clients in a broadcast (or targeted) fashion.