The first 4 (Head First Design Patterns, User Stories Applied, Design Patterns and Refactoring) I have finished reading and can highly recommend, the last 4 (xUnit Test Patterns, Test-Driven Development, Code Complete and Implementation Patterns) I am currently reading.
Check out this exercise for writing better object oriented code. It contains a list of 9 rules, some of which are quite extreme. Let’d be clear on this: These aren’t rules for object oriented code. Not all OO code has to follow all these rules. This exercise is more like practising. Writing code that follows these rules will train your mind to think in an OO way.
Here’s a good post describing four things that make a developer great.