How about
Gang of Four -
http://en.wikipedia.org/wiki/Design_Patterns It's one of the
best sources of design
patterns out there. I highly recommend this one
Fowler and Liskov also have some really nice books on OOP.
What exactly are you looking
to learn? (That is, can you give us some insight as to what you actually know about
OOP so that we can go from there? Are you already familiar with what an abstract class is,
inheritance, and so on? Or do you want to learn the basics?)