OOP

No this post is not about the famous hit Oops! I did it again. It's about Object-Oriented Programming in Java.
Some of you might think, as I recently created the new quangntenemy teaches Java 2 applet challenge, which is mostly about OOP in Java, I should be very good at it. Well, the fact is that I am just above the beginner level, as classified by Java BlackBelt.
While roaming around the Internet looking for resources in preparation for the next belt, I came across this tutorial at Java Boutique. Very good one ;)
I am looking for more tutorials like this, or better, some ebooks about OOP in Java at intermediate level. If you have any recommendation, please let me know :)