OSDev.org

I want to study several examples before deciding what method to enable memory management in for my group's kernel.  The targeted environment is an x86 platform that may eventually be migrated to x86-64 if I can get my hands on a Hammer chip someday.  For now though, I would like it if someone could show me a mature memory system that isn't that difficult to tear apart.  So if anybody has a good example or good links, especially a tutorial that takes an entire system and describes its code, that would be nice.