How do I learn C# fast(er), already knowing C, Java, C++, etc.?

If you already know the above languages, I would suggest that you assume that you know the language already and dig into the more interesting .NET stuff, such as CLR via C#, which I can reccommend very highly (but not so sure how much it applies to Mono though). The gaps in your language knowledge will fill themselves in.

I suggest you read C# 3.0 in a nuthshell. It is especially aimed for programmers of other languages. Here is a review by Jon Skeet

Collect "Mono: A Developer's Notebook", or "Practical Mono" or "Open Source .Net Development: Programming with NAnt, NUnit, NDoc, and More".

The second one is very well-written.