If you're interested in viewing some Agatha Christie, Ngaio Marsh and Gladys Mitchell first edition covers, check out this link to my friend Phil's blog - Slow Speedy Death.
I recommended one of my favourite authors to Phil last year - Pamela Branch. He bought a first edition of Murder's Little Sister (pictured - cover art by Sax) on that recommendation, only to find Branch's writing doesn't draw him in the way she does me. I still feel bad about that... Although it must be said that Murder's Little Sister is not her best.