Assembly

• Christopher Browne's assembly language resources
• Mac OS X Assembler Guide (Covers PowerPC instruction set/more)
• slide preso with a really basic assembly/etc intro (also explains gcc toolset/gas/etc)
• Gene Davis's Real Geeks Assemble: Beginning Assembly Language (on PPC) ** chapter 1 ** chapter 2
• VM Instruction set (itself an assembler language basically)
• JVM Instruction Set from Compiling Pascal to Java
  

Tools

• binutils including objdump which can disassemble native code (useful for seeing just how good/bad the code you generated is)