I don't know of any real valuable online resource. If you want a full coverage of what Sun expect you to deliver then I recommend you buy one of these:
everyone with 95%+ I know used "Thinking in Java", "Effective Java" and "Design Patterns", and no specific SCJD literature. The drastic success (not only in SCJD) of people who learned with these resources encouraged me to write this learning path.
If you have Andery Monkhouse book, you do not need the second one recommended by Darya. Monkhouse gives very good starting point but be creative and follow your assignment very carefully.
The SCJD forum is definitely the place to discuss some important aspects. But why do you think are these books for ? You better get those books for the whole picture .