Brillium, Inc. uses .NET
Microsoft has done an incredible job of keeping the .NET Framework powerful and stable. It is well designed and keeps getting more robust with each release. It isn't the most popular technology in this space, but I think a good case can be made to use .NET in many new projects.
Foundbite uses .NET
As we started on Windows Phone we use C# and .NET for most of our apps and sites. Being a small team of 2, using .NET enables us to work on each part of the service without having to switch to different languages.
danielkovacs uses .NET
I use .NET alongside with C# since my university studies, and I really enjoy it. Especially .NET Core, which is the best thing that happened to Microsoft since... ever.
Mooophy uses .NET
Server side development language and frameworks: ASP.Net MVC 4, Asp.Net WebApi 2, Razor View engine, Moq, Entity Frameworks, etc.