x86 instruction set / optimization resources

Nothing too fancy if you're not into developing x86-related stuff (or don't even know what x86 is!), but nevermind, here are some nice resource I just want to write down, 'cause they're really worth it:

http://sandpile.org/
http://penguin.cz/~literakl/intel/intel.html
http://www.agner.org/optimize/

Got some other cool x86 resources to share? Let me know!