I didn't notice that many authors I hadn't heard of, interestingly enough. Whether that means that I know more authors than I thought, or that bookstores are drawing upon a smaller, less diverse pool of authors--well, I can't say. But one thing I did notice was the big difference in book covers.
What I saw first was the different covers for Airhead by Meg Cabot. The American hardback is on the left; the British paperback (yes, paperback!) is on the right.
Quite a difference, I'd say. While I don't think either cover fully reflects the book, I think the American one certainly draws your eye moreso than the British cover.
There's also plenty of covers that are great for their respective book, both in the American and British editions. For example, Rick Riordan's Battle of the Labyrinth, the latest book in the Percy Jackson and the Olympians series:
Both good, I think. It's interesting that the British edition gives so much prominence to the series title, versus the American cover.
Finally, some books have gotten a lot more prominence in Britian than the US, it would appear. There's at least two different paperback covers of The Book Thief by Markus Zusak, as well as a different hardback cover than in the US.
Perhaps the fact that Zusak is Australian has some bearing on this, or the fact that The Book Thief was originally published as an adult title in the UK. But it's interesting to see the different takes on the same book.
If you like these questions about book covers, why not visit Jacket Whys? It's a great blog for comparing and contrasting the ways books are marketed through the book jacket.