The Millions has a side by side comparison of book covers from the last year as they appeared in the US and UK. Can you spot any patterns of national taste in the designs? It would be interesting to see a comparison of sales in the two regions, to get a sense of the effectiveness of the respective covers in their different markets.
They have previous years as well: 2011, 2010, 2009, 2008, 2007.
To delve further into book design and the US vs. UK design aesthetic:
Fully booked : cover art & design for books / [edited by Robert Klanten, Matthias Hübner – Z271.3.B65 F85 2008
Faber and Faber : eighty years of book cover design / Joseph Connolly – NC973 .C66 2009
Puffin by design : 70 years of imagination, 1940-2010 / Phil Baines – Z325.P84 B35 2010
By its cover : a history of the American book cover / Ned Drew, Paul Sternberger – NC973.5.U55 D74 2005