Folio had a great article about a month ago about "turkeys." That is, magazines that underperform. The article discusses how covers do or do not communicate the content and by so doing compel a reader to pick up the magazine.
The same applies to books. Really, to any product. Packaging is hugely important. If you've made a great product but can't get it off the shelves into consumers' hands, what's the point?
My tastes skew literary. I like quirk, which tends not to get too much screen time in commercial fiction, where formulas are more adhered to. I like commercial fiction, too, and am in fact of some unpopular opinions about how literary and commercial should meld. But that's another post. Covers like this appeal to me:
But, you say, that's...weird. It doesn't tell me anything about what the book's about. True. But, first of all, this is a story collection, so it's not "about" anything. Second, this is effing quirk, people. This is going for it. The cover promises me quirk, which I like to read. As a lover of quirk, you couldn't beat me off this book with a stick.
(Note: the three following books are Janet's)
Gary Corby's THE PERICLES COMMISSION
Not only does this cover have great colors and composition, it immediately tells you the two most important things about the book: it's a mystery (note the shifty eyes) and it's set in ancient Athens. No, put that stick away. It's not going to work.
Sean Ferrell's NUMB:
Who doesn't love a white cover? This book is about a man with amnesia and how he rediscovers himself. And look. This guy on the cover has no head. Coincidence? I think not. This cover promises the unexpected. The book 100% delivers.
Evan Mandery's FIRST CONTACT
This is quite possibly the funniest book ever written. The cover tells you this, and also hints at the circular and slightly chaotic story inside. This is a book for lovers of Vonnegut, and I think the cover screams "DID YOU LOVE HARRISON BERGERON?!"
Unlike products like clothing, where the sum total of the piece can be readily displayed (Those shorts are just shorts. There's no deeper message.), books require an investment. You have to take the time to read some of the book to appreciate what's written. The only way to get someone to make that investment is to convince them that the content will interest them. The only way to do that is with a kickass cover.