* ASP.NET for web with SQL Server + EF for the database and data access
* Xamarin for mobile and OData for data access (back to our ASP.NET sites)
The CLR is great because it's always been fast enough for our applications and every so often you get something for nothing. For example, CLR 4.5 brought better GC and RyuJIT is bringing better code generation. NET Native might give us even better performance.
LINQ is amazing if you know your IQueryables from your IEnumerables and the difference between an Expression<Func<T, bool>> and a Func<T, bool>.
Hosted in a private datacentre, not using Azure but we've got our eye on it (provisioning resources in the Azure Portal seems to get easier and easier than doing it ourselves).
New Relic for monitoring the web sites.
My biggest gripe (and it's not that big) is that within the Microsoft ecosystem/community everything works great but once you go outside it things are less well supported. Some less-popular-but-wow-that's-useful Javascript libraries don't come as NuGet packages. New Relic's .NET monitoring seems good but second fiddle to their other stuff.
After that I'd say Xamarin is letting the team down. Every second or so release of theirs fixes two bugs but adds another one.
Keeping an eye on Application Insights. It looks like it integrates nicely with Visual Studio Online, and VSO/TFS actually looks quite nice in parts (e.g. Bamboo for CI is largely geared towards Java apps not .NET but TFS' Release Management looks promising). I have my eye on VSO/TFS too but right now it looks like pros do not outweight the cons vs. our Atlassian applications.
If you've got enough processing power and memory and a fast SSD to run Visual Studio + ReSharper it's coding heaven.