I'm currently reading a very good and, almost inevitably, out of print novel by David Garnett: A Shot in the Dark (nothing to do with the Pink Panther movie of the same name). It's an old Penguin paperback, with a cover by David Gentleman.
Gentleman has a long history as an artist, and there are a number of interviews with him available online. He does lithography, woodcuts, ink and watercolours, and has designed numerous stamps as well as book covers.
To begin with, here are some of his Penguin Modern Classics (click for bigger versions of almost everything here).
Then there are some of his other Penguin designs.
He also designed all of the New Penguin Shakespeare covers in the 1970s: here they are displayed on an advertising sheet from the era.
Gentleman's own travels have yielded a number of art books...
..and this talent for landscape has been used to great effect on the Faber covers for gun-mad Lawrence Durrell and others.
He's also collaborated with previously un-noted Hero of this Blog Russell Hoban (anyone who can write books as brilliant and as different as Riddley Walker, Turtle Diary and the Frances the Badger series is highly regarded around these parts).
And here's the bit at the end of the post where the other covers I've found by him get all jumbled together...
Ebury published a collection of Gentleman's artwork in 2000, cunningly entitled Artwork.
The cover is a detail from one of Gentleman's many stamps.