Designing Objects: Advice

I am a rather competent programmer and have been for many years so my issue is not with the designing of procedural/modular programs but with the design of object oriented programs. I just have a massive issue thinking in this way and was wondering if there is any on-line material to aid in this respect, I mean anyone can program OOP if they are already given the base classes/methods I just want to get a lot better at designing it.

Please anyone in the field...help a newbie out. :)

This is a good post for Reference books for Object Oriented Programming and Design Patterns : starting OOP (http://stackoverflow.com/questions/5730345/reference-books-for-object-oriented-programming-and-design-patterns)