Introduction to ASM

Anyone know a good way to start learning ASM? What's the best ASM language for x86?

http://homepage.mac.com/randyhyde/webster.cs.ucr.edu/www.artofasm.com/index.html

Oh, it doesn't look like AoA has been updated to 64 bit, but all you really need to know is that the 64 bit registers have the prefix r, e.g. rax, rbx, etc. There are a bunch of other changes but they aren't relevant to a nub.