I took the IBM 486 OOAD with UML exam today, very pleased with the score as well. The topics on the exam are quite tricky, and took a fair amount of studying. The most useful study materials I used were:
UML and
Patterns (Craig Larman)
UML Distilled (Martin Fowler)
Use Case Modeling (Bittner and Spence)
The Unified Modeling Language User Guide (Booch)
Whizlabs 486 Exam Simulator
Also of some use were:
Object Design (Wirfs-Brock and McKean)
The Unified Software Development Process (Jacobsen)
Developing Software with UML (Oestereich)
Writing Effective Use Cases (Cockburn)