Readerville has a great thread in their forums called Most Coveted Covers, a frequently updated list of well-designed book covers. Related are Edward Tufte's book reviews, Book Design in Canada from Cardigan Industries, and an interview with Chip Kidd on Identity Theory.
There's a bunch of really well designed covers in the edition galleries of orwell.ru for Animal Farm, 1984 and others. The covers are from a bunch of different countries and times, so you can compare the different design trends.
It's sort of related, but there's an article on the decline of the quality of magazine covers.
I've always been quite obsessive over book cover design -- often just as important to me than the design itself, though, is the texture of the cover (glossy is my worst enemy).
My favorite cover design, ever? The Vintage International Lolita. Simple and appropriate, and it feels so good under my fingers.
Re: Dean Allen's essay: I think he's completely right, especially about The Porcupine's Quill. The interior typography and design is exquisite, but the covers (and actually, the presentation faces) are both ugly an inappropriate.
This thread is closed to new comments. Thanks to everyone who responded.

