I absolutely love looking through artists' sketchbooks. The informal drawings of a great illustrator can be an excellent way to see the world through her or his eyes. Tom Judd's Everyday drawing project, consisting of a page a day for a year, is mind-blowing. (His new project is called Once-A-Week and that week's drawing will be auctioned every Saturday on eBay.) From his description of Everyday:
365 PAGES AGO I HAD A VERY SILLY IDEA. Draw a page everyday for one year. Each day I spent around 1 hour on the page, sometimes more, sometimes less. There was never any planning or preparation, I would just go at it whenever I had a spare moment in my day and had something I needed to write or draw. Some of the drawings are observational and some are just plain weird. Monsters and things seem to crop up a lot (robots too). I have no explanation for this and don't really care because its my book and I drew what ever I wanted on that particular day.