Newbie programmer here. I want to really learn C#. Other than VS what other IDE's are there?
Mono is probably the next most popular IDE after Visual Studio. It's not bad, I've used it sparingly over the years. But I think you'll find that you're better off sticking to Visual Studio unless you have a very convincing reason to not use it. Especially given Microsoft provides the Express edition free of cost.
If you want to really learn C#, then move on to the professionals in the same field so that you can get enough information on what you need to know. From online you can find such professionals very easily by searching Google.