C#. Nothing like having access to a bunch of frameworks / initiatives that are maintained and supported by MS -- for free. There are way too many for a single person to specialize in, though, unless you are a super genius. The alternatives are almost all open source and almost exclusively community maintained. Personally, I would rather use a bunch of libraries MS has a vested interest in maintaining and supporting for free. If choosing between select few, the learning curve on Entity Framework is low, and that will cover all of your database needs. So, with just C# and Entity Framework, you can cover most of the things you are going to want to be able to do with a relatively low learning curve.
Some have mentioned a directive of everything moving to JS, which I don't agree is the case; it is merely an agenda -- other languages are not going away. Further, JavaScript is an extremely terrible and difficult programming language. Speaking from the perspective of the root language and not just using the various frameworks that exist to wrap around it to mask how terrible it is, at least. Luckily, the frameworks for JS are generally good and easy to use, so that may be a moot point. To accommodate the agenda in C# there is, of course, a relatively unknown MS offering called ClearScript, which leverages Google's V8 engine to offer interoperability between JavaScript (among other languages, as well) and C#. The documentation is pretty poor, though, and I haven't used it as a result of that and just finding out about it a couple of days ago, but, again, an example of the benefit of going with C#.
VB is the only C# alternative in my book; their functionality is practically identical (there are a few underlying differences with them related to compiler-generated attributes / reflection / a couple of things that are possible in VB and not C# related to declarations / overloading IIRC, too, but they are generally consistent with each other), but the syntax is too different from most other languages with VB for me to have chosen it, at least, and I think that's a growing trend so resources for C# seem to outweigh resources for VB. Libraries that can be used in C# can be used in VB. Personally, I think VB is going to go away at some point in the distant future; MS doesn't even bother with showing VB examples on their tutorials for any of their modern offerings most of the time.
If you are going web and don't want to do ASP, I would choose PHP, but you have to be prepared to deal with a lot of things yourself working with the root language.
Also, if you like assembly, there is System.Reflection.Emit, or System.Linq.Expressions. While not assembly, Emit lets you output compiler commands directly, and Expression is, for all intents and purposes, a wrapper around Reflection.Emit that abstracts out some of manual optimizations you would have to do through emitting the IL code (though you can often Emit faster / more efficient IL yourself, Expression trees will take some of the burden of maintainability off of you and would let you leverage future optimizations to the underlying IL produced by the trees when MS makes improvements without having to modify your code).