If you'd like something pretty to keep your pen and notebook together, here's how to make your own cheap pen pocket for your notebook.
This is a great little DIY sewing project that will keep your pen and notebook together wherever you go, for just a few bucks. All you need is a long black elastic ribbon, a sewing machine (or the willpower to do a bit of manual sewing), and some black thread. It's pretty easy to make; all you need to do is loop the ribbon around and overlap the edges, long enough for the overlap to fit the length of your pen. Then just sew the sides together to turn it into a pocket. You can then wrap the elastic loop around the edge of your notebook, pocket on the front, as shown above, for an easy pen holder. Hit the link for a PDF of detailed instructions.
Moleskin Pen Holder [Gnat Gnat]