From facebook's own figures:
1. Farmville (63 million)
2. Causes (35 million)
3. Café World (28 million)
4. Mafia Wars (26 million)
5. Happy Aquarium (24 million)
6. Pet Society (21 million)
7. FamilyLink.com (21 million)
8. Yoville (20 million)
9. Texas HoldEm Poker (19 million)
10. Farm Town (18 million)
Set up your app to recruit facebook friend networks and explode!
