I find that illustrating simply using various grades of pencil to be a great pleasure. Omitting the complicated techniques associated with traditional media, or the need of digital tools, grants me the freedom to focus on the creation of an illustration focusing entirely on tone, highlights and shadow.
This kind of illustration works beautifully for book interior illustrations.
I also enjoy simply putting pencil to paper and seeing where the imagination takes me. It never ceases to amaze me what the subconscious can conjure up.