While investigating Authenticode, I become curious about the Portable Executable format. This is the file format used by all Windows executables.
Here is a good overview in the context of .Net. And here is the referenced image which is missing from that post (originally http://jfmasmtuts.blowsearch.ws/Ch2/peheader2.jpg):
This missing image turns out to be part of a fantastic overview of the PE architecture. While the original article appears to be long gone, it lives on in an archive (and as a PDF in my own archive).
Here is a significantly more dry introduction, from MSDN.
