Links to various documents about Z80 machine language (assembly language).
The Undocumented Z80 Documented - Nice document that summarizes all Z80 opcodes (including the undocumented ones).
Document: z80-documented.pdf
Reference: http://www.myquest.nl/z80undocumented/
Full Z80 Opcode List Including Undocumented Opcodes - Nice table with all Z80 opcodes.
Document: Z80_OpList
Reference: http://mdfs.net/Docs/Comp/Z80/OpList