I always find books more helpful then random sites.
First of all is what is your current level?
1. Are you speaking of only core JAVA? A good book like say Deitel and Deitel is necessary for a solid background.
2. The head first series of books are also good if you intend to start from the very beginning and then move up.
3. Then you can move on to say looking at a few datastructures and algorithms with java books.
4. I guess once you are done with this you can move to related technologies..
JSP,Servlets or frameworks like JSF and Struts.
If you are a bit more specific on what you are looking at I might be able to help you