As a designer, I'm a sucker for a well-designed book cover. I will gladly spring the extra dollars for the book that has the nice typography in lieu of the tacky movie tie-in book covers. I've been known to buy books I already own by virtue of the cover. The recent Peter Menelsund book covers for Dostoevsky's novels made me repurchase the entire series, though I've yet to reread them.
I had the same weakness for a well-designed CD cover, when that media was relevant. I remember flipping through the stacks of CDs at Dr. Wax in my twenties, when I pulled out a copy of Social Distortion's Somewhere Between Heaven and Hell. It's not a great design by any means, but it has a nice energy to it. The hipster skater kid standing next to me took notice and said “that music is exactly like that cover”. I bought it on that endorsement alone. He was right, what you see is what you hear; raw, unflinching with a rebellious spirit to the music.
The same can be said of the re-issue of Cormac McCarthy's backlist, designed by David Pearson. McCarthy is one of my favorite writers and the cover series is breathtaking. Gorgeous typography, bold colors that jump off the page to smack you in the face, and to paraphrase the skater kid, look exactly like what you are about to read. McCarthy's work has never been represented in such an evocative manner, capturing the spirit of the writing and the time in which the stories occur. Stunning work.