Here's some topics you guys can start up if you want.
1. Where to find more links to more optical illusions. 2. Is it important to really understand the inner workings of using unicode as a way to write your code. 3. What is the relation between the Set interface and TreeSet. Does TreeSet accurately implement the Set interface. 4. How does the post and pre-fix incrementers really work? 5. If you could fix and change one thing in the J2SE APIs what would that be.
I'll try to think up some more for you guys later. I'm actually on vacation right now.