I love seeing sketchbooks that are really sketchy– not finished, perfect works on each page, but a mish-mash of lines and colors, where you can really see the artist working things out in a process.
The one below is from ANOBELISK, where the artist, an illustration student, says:

“I fill a sketchbook with images and text every month or two. They are invaluable tools for supplementing my imperfect caches of memory and inspiration. Beyond that, their pages act as snapshots of my state of mind, my daily affairs, my goals, and my fears. Patterns of material and subject reveal the rhythm of my week, in terms of the demands of my classes, and of idle and active imaginings that fall outside of what is asked of me.”

 

The sketchbook itself is a 5×8″ version of the Pentalic Illustrator’s Sketchbook.

See more at October 2012 Sketchbook.