Catlike Coding has many well written tutorials. The tutorials on rendering and hex grids are especially good.
P4Merge - The (free) Perforce merge tool, P4Merge is hidden in the installer for the Perforce suite. It is the best standalone merge/diff tool available.
The Nature of Code - Uses Processing and Java, but the code is simple enough to transcribe to C# easily. Chapter 1 - Vectors is a very good introduction to vectors and linear algebra in a programming context.
Game Programming Patterns - Most of the content in this book is too specific and beyond the scope of this class, but I add it here if you're curious.
WikiWikiWeb - The first and original Wiki, created by a bunch of nerds to talk about nerdy programming things