Binni Shah posts two great links for reverse engineers on x86 systems:

1. A Crash Course in x86 Assembly for Reverse Engineers (PDF)
   

   The hardest part of learning x86 assembly in 2013 is finding good tutorials. As the popularity of low level languages decreases the incitement to create fresh up to date tutorials is limited.
   At the same time x86 assembly is critical in many security related fields such as malware analysis, vulnerability research and exploit development.

   This document was created to address the lack of tutorials in a fast, pedagogical and cheap manner. While it is not a complete introduction, it addresses enough to prepare careful
   readers with the necessary knowledge base to be able to decipher non-obfuscated assembly. And it does so within less than thirty pages.

   For pedagogical reasons focus is kept to what the reader assumedly knows about C or C based languages (like Java or C#). Hopefully this minimizes the confusion that usually
   appears when people are trying to learn a stack based language for the first time.

2. Reverse Engineering x86 Processor Microcode (PDF Slides)
   

   Summary
   • We built a framework for microcode reverse engineering
   • We reverse engineered substantial parts of the encoding
   • We implemented meaningful microprograms from scratch
   https://github.com/RUB-SysSec/microcode/