Here's a list of the top sellers in hardback books for 2011 and their sale numbers as noted in Publishers Weekly. Reviewing the list you can see that it pays to be serial writer. It also shows how hard it is for a new writer to break into the top numbers list.
1. Cabin Fever (Diary of a Wimpy Kid #6). Jeff Kinney. Abrams/Amulet (3,321,388).
2. Inheritance (Inheritance Cycle #4). Christopher Paolini. Knopf (1,811,022).
3. The Son of Neptune (Heroes of Olympus #2). Rick Riordan. Disney-Hyperion (1,781,189).
4. The Throne of Fire (Kane Chronicles #2). Rick Riordan. Disney-Hyperion (1,187,604).
5. Destined (House of Night #9). P.C. and Kristin Cast. St. Martin’s Griffin (625,000).
6. Middle School, the Worst Years of My Life. James Patterson and Chris Tebbetts, illus. by Laura Park. Little, Brown (543,254).
7. Every Thing on It. Shel Silverstein. HarperCollins (511,389).
8. If You Give a Dog a Donut. Laura Numeroff, illus. by Felicia Bond. HarperCollins/Balzer + Bray (508,884).
9. City of Fallen Angels (Mortal Instruments #4). Cassandra Clare. S&S/McElderry (495,766).
10. Tales from a Not-So-Talented Pop Star (Dork Diaries #3). Rachel Renée Russell. S&S/Aladdin (492,832).
11. Silverlicious. Victoria Kann. HarperCollins (481,227).
For Paperback Editions...
Again, once you have an audience they want to read more of their favorites. Movies beget books and books beget movies.
1. Breaking Dawn (Twilight Saga #4) (trade and mass market media tie-in editions). Stephenie Meyer. Little, Brown/Tingley (753,888).
2. Witch & Wizard (mass market). James Patterson and Gabrielle Charbonnet. Little, Brown (656,665).
3. Phineas and Ferb: Across the 2nd Dimension. Disney Press (516,007).
4. Pinkalicious: Pinkie Promise. Victoria Kann. HarperCollins (457,416).
5. The Last Olympian (Percy Jackson and the Olympians #5). Rick Riordan. Disney-Hyperion (448,672).
6. Phineas and Ferb: Agent P’s Top-Secret Joke Book. Disney Press (403,950).
7. Race Around the World (Disney/Pixar Cars 2). Random House/Disney (356,822).
8. Fang (Maximum Ride #6) (mass market edition). James Patterson. Little, Brown (330,806).
9. African Cats: A Lion’s Pride. Disney Press (296,077).
10. Beastly (movie tie-in edition). Alex Flinn. HarperTeen (276,033).
11. Judy Moody and the NOT Bummer Summer (movie tie-in). Megan McDonald, illus. by Peter H. Reynolds. Candlewick (270,040).
If you would like to read the complete list of the top 100 best sellers in both categories, here's the link to do just that.