Here are some examples of sketchbooks that I've gathered as I've been thinking about this issue of cross-disciplinary design
The following examples are chosen essentially at random from some well-known artists' sketchbooks
The original "renaissance man" - an artist, scientist, architect, and engineer. He kept wonderful sketchbooks full of interesting drawings and writing. You can find huge numbers of images on the web.
From http://www.unmuseum.org/leosketch.htm: In many of his books Leonardo employed a backwards form of writing that could only be read with a mirror. It is unknown why he did this. Some historians speculate he did it to keep his writings private, others think that because he was left-handed he just found it easier and faster to write this way.
You do not have to emulate this writing style!
Picasso is reported to have said "... I picked up my sketchbooks daily, saying to myself `What will I learn of myseld that I didn't know?' "
These images are somewhat lo-res, but if you search for Picasso sketchbook you can find all sorts of things on the web
I especially like his travel journals / sketchbooks (Personally, I like them much more than his paintings...)
Known primarily as a sculptor, he also made wonderful drawings. His drawings of sheep are really fun to try to emulate. Look at them closely - they are made totally of scribbles. He used looser scribbles for light tones and denser scribbles for dark tones.
Another artist whose style is fun to try to emulate. His sketch-like drawing style is also used in his paintings.