Tom Gauld is a wonderful Scottish illustrator and comics artist whose work I only discovered recently. British Guardian readers will already know his work, however. He co-runs the small Cabanon Press with fellow comics artist Simone Lia.
He has done a number of wonderful book covers. This first is for the Penguin Graphics Classics series (as featured on this blog in posts about Dorothy Parker and Jack Kerouac) edition of Dumas' The Three Musketeers.
This image is only part of the story: the cartoons extend to the back cover, the spine and the front and back flaps, too.
Gauld has also done the covers for a number of Jose Saramago's novels for Harvill/Vintage. (With everything shown here, click for more detail.)
He has also done the covers and interior art for recent editions of Ted Hughes' The Iron Man and The Iron Woman for Faber & Faber.
Interior art from The Iron Man can be seen here.
Another pair of covers cover British culture and history: The Tribes of Britain by David Miles and Our Island Story by H. E. Marshall.
Finally, here are Tom Gauld's own thoughts on cover design, from a cartoon in the Guardian.
(You also need to look here for a series of his cartoons about various writers at work, Parker included).