First a little about myself. I have been developing some part of an enterprise system in Java since 1998. I have had experience with RMI, JDBC, Swing, Servlets, ADF, and OAF. I am currently studying for my Sun Certification Java Programmer 6. Here are some links I have found useful in Java developing:
http://java.sun.com – This is ground zero for Java Development news and links.
http://java.sun.com/javase/6/docs/api/ – API Specification for Java 6 SE. I have this page always open when I am programming.
http://java.sun.com/javase/downloads/index.jsp – Download JDKs, documentation and development bundles.
Those are what I can think of now. I will post more as I think of them.