Check out Tore's site for a free C# e-book: CSharpBook at Programmers Heaven
I've spent 3 minutes skimming through it and it seems to be a nice introduction to C# and .Net. This (oversimplified) conclusion is based on finding information about boxing/unboxing, immutable strings and generics.
By the way, while you're there, look around the site and subscribe to the newsletter or RSS feeds if you want updates. And if you find any of the advertisements interesting, click on them and buy whatever product they sell. Tore is a nice guy and makes his living on just that.