We've always counted on SQL Server as our database backend. It has served us well over the years. It isn't the cheapest part of our stack, but with the plethora of tools provided by 3rd parties, we have found an incredible and scalable method of keeping our data available and easy to maintain.
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.