I uniformly found anything but the manufacturer's references to be verbose and slow. I learned Z-80 assembly from Zilog's instruction set reference, and 6502 assembly from the Synertek reference. Ditto the 68000.

I never really learned x86 assembly because I started with some awful Scelbi book.

BTW, I used assembly in a real-world project about two years ago, and one of my cow-orkers was using it yesterday. It's anything but dead.

Richard Haskell's book ( http://www.amazon.com/Apple-II-6502-assembly-language-tutor/... ) was the one that finally made it click for me. Zaks's book was an older one -- targeting the KIM-1, IIRC. It didn't have any Apple II-specific content, but it was still interesting to read once I'd worked my way through Haskell's book.

Richard Haskell is still writing accessible introductory books for Verilog and VHDL. His new books look pretty good, but they came along a bit too late to help me this time.

I read Zaks' book back when, but it was rather dry and these days I'd recommend Machine Language for the Commodore 64 by Jim Butterfield instead.