http://www.comlab.ox.ac.uk/archive/cards.html
This page offers low-level programmers a central location for the quick reference cards provided by chip manufacturers for microprocessor programming. The maintainers of the site have re-formatted reference cards from different manufacturers into a common format, which allows programmers to quickly find the processor-specific information they need (once they have learned the format). In addition to cards describing chips from many different manufacturers, a number of re-formatted programming language reference cards are provided.