99 Bottles of OOP
The intro sold the book to me but I'm a bit reluctant to buy it because of the fact that it uses Ruby. I've just started working with Java (straight from University last year) and I've come to realise that in comparison to other OO languages which have evolved their syntax (C# & Python) Java hasn't. I doubt it'll help me with Java. I've already invested in a few books and test engines, mainly for my Oracle certifications.