It's been a while (more than a decade, actually) since I worked seriously in C#, and so I had rather lost track of what's going on in that community.
But recently I stumbled upon BOTR, the DotNet Book Of The Runtime.
What a great resource! Each article is clearly written and useful on its own, but most of them lead further with many references to even far more detailed information about DotNet internals.
I have no idea if or when I'll ever be back in the C# programming world again, but it is certainly pegging my geek-o-meter to dig through this treasure trove of system programming details.