From MyAnimeList:
ICv2 has released a list of the top 25 North American manga properties for the first and second quarters of 2011. The chart is based on interviews with retailers, distributors, and manufacturers.
rank / title / (publisher)
*1 Naruto (Viz Media)
*2 Bleach (Viz Media)
*3 Vampire Knight (Viz Media)
*4 Black Butler (Yen Press)
*5 Death Note (Viz Media)
*6 Black Bird (Viz Media)
*7 Rosario+Vampire (Viz Media)
*8 Fullmetal Alchemist (Viz Media)
*9 Dragonball & DBZ (Viz Media)
10 Soul Eater (Yen Press)
11 One Piece (Viz Media)
12 Maximum Ride (Yen Press)
13 Alice in the Country of Hearts (Tokyopop)
14 Hetalia (Tokyopop)
15 Yu-Gi-Oh! (Viz Media)
16 Pandora Hearts (Yen Press)
17 Bakuman (Viz Media)
18 Fruits Basket (Tokyopop)
19 Dengeki Daisy (Viz Media)
20 D.Gray-man (Viz Media)
21 Yotsuba&!! (Yen Press)
22 Ouran High School Host Club (Viz Media)
23 Shugo Chara (Del Rey Manga)
24 K-On! (Yen Press)
25 Highschool of the Dead (Yen Press)
Obviously, it's incredibly unsurprising that Naruto and Bleach (regardless of what you might think of them) are topping the list. What follows, though, is extremely interesting because I don't think it resembles Japan's list at all.
The most obvious difference is the lack of domination by One Piece, which is understandable. I wouldn't expect One Piece to really resonate with American tastes.
Vampire Knight is super surprising, because it's a very shoujo title that I can't see appealing much to guys, which is unlike some of the more popular shoujo titles in Japan. This means that, not only is it likely the manga of choice for female fans, but that it has enough numbers to beat some of the bigger titles. This is the same sort of thing with Black Butler, which I'm sure we can all agree is pure fujoshi-bait.
Death Note at number 5 in the year 2011 is kind of amazing, because it's been finished for years now.
Black Bird is a surprising title because I've never heard of it.
Then we have Rosario+Vampire, which is a surprise because it's the only fanservice title in the list, but it appears surprisingly high.
Dragon Ball, well, is Dragon Ball.