I've come across some interesting links recently that explore the notion of drawing as a meditative process and a way to enhance one's observational skills. "Drawing is Thinking" is a book by the graphic designer Milton Glaser. The book has a short introduction, followed by an interview with Glaser, and then the rest of the book is a sequence of small images covering subject matter spanning his entire career as an artist and graphic designer. He discusses the central thesis behind the book in this short video, which shows him drawing an image of Shakespeare as he talks.
Another cool link is a pdf booklet by the artist Michael Nobbs, who also maintains a blog. It's written in a similar vein as "An Illustrated Life", gives helpful tips for keeping a daily sketchbook, and gives some useful references for followup reading.