Re:Refactoring (Score 1)

I very much agree. "Design Patterns" and "Refactoring" complement each other very nicely.

I would add the Extreme Programming books to the list, especially "Extreme Programming Explained" (Kent Beck) and "Extreme Programming Installed" (Ron Jeffries, Ann Anderson, Chet Hendrickson).

Also by Martin Fowler, "UML Distilled" is very useful.

These books (as well as "Refactoring") are especially useful for libraries because they're short enough to digest within the typical lending period and will teach you lots without necessarily having to refer back to them all the time. That said, they make great references as well.