An in-depth look at OCaml's x86 code generation. Some of it's pretty hardcore. One obvious observations is that it can generate relatively fast assembly because you don't need to check types at runtime.
This bit on the addition function near the end is rad: (It's actually more subtle than this - to perform the mathematics quickly, OCaml uses the x86 addressing hardware in a way that probably wasn't intended by the designers of the x86.)
Internal representation of strings.
I got hopeful looking at the MLDonkey screenshots that it could make fancy-looking Windows native GUIs, but that appears to be written in Java.