Sketchbooks remain an integral part of my process.  A lot of ideas often first take shape in them.  It is a playground of sorts, and I never get tired of visiting them.  
 
I often purchase sketchbooks from thrift stores, I like the idea of a second life given to them!  However, I take my work seriously and when I want something polished and lasting, I go to Stillman & Birn.  Please follow the link to find out more about them, I cannot speak highly enough about their quality and who they are as a company, just terrific people.