I've been doing loads of stuff in my sketchbook lately and for a little inspiration break I look to this book
'Graphic: Inside the Sketchbooks of the World's Great Graphic Designers' which contains extracts of some sketchbooks from some pretty amazing artist. I thoroughly recommend if you're at university studying a creative subject. I wish I had this where I was at Camberwell.
A lot of the artists say they either never kept a sketchbook until very recently, or kept a sketchbook but burned it when they'd finished with it, or better still they don't keep a sketchbook, but just find a piece of paper and draw on that.
The later is what I did, and felt like an idiot when I came in with folders of work instead of tiny little sketchbooks like my peers. There's nothing wrong with it! I felt constrained by the dimensions of my sketchbook and therefore hated drawing in there. Scraps of paper on the other hand, they can be as big or as little as you want, whenever you want!
anyway, have a flick through when you're next in Waterstones (or any other good book shop) but I think Waterstones is suffering at the moment so I try to shop there instead of Amazon (yuk).click here to buy