UML Distilled
The subtitle for this book is “A Brief Guide to the Standard Object Modeling Language”. And boy, is it every brief: only 150 pages (excluding the appendix, bibliography, and index).
Fowler does a great job and quickly and efficiently teaching the UML diagrams most often used in the real world. Because it is so concise, it is easy to pick up for a quick refresher.
I would probably stop short of recommending it, though. If you find yourself doing a lot of diagramming and wanting to be more expressive in what you put together, pick this up. If, however, UML is something you only use occasionally during a session at the whiteboard, you probably already know enough to get by.
