i previously did a post on 'my penguin' (here), a set of books available from penguin that come with plain front covers which you then do yourself (or not, if you wish). above is my cover for alice in wonderland which i did for my brother (who first showed them to me).
on the my penguin website they have a gellery of covers done by other people who have bought them. below are just a few of my favourites, of which there are many.
it is a great idea, and i still highly recommend them!
link to my penguin