Definitely this one. Years ago, I used Sun's Developer Forums, but I found their community to be neither helpful nor friendly.
My Java guru is Bruce Eckel, so I often reference his online book, Thinking in Java. (A hardcopy of this book was my primary text for learning Java.)
Of course, there's the indispensable Java API. If I'm nitpicking, I might check the Java Language Specs.
I don't use Google (-insert collective gasps of astonishment-). Instead, I use Metacrawler, which uses Google in conjunction with other engines. When searching for Java information, this usually brings me back here to JavaRanch or to JavaWorld.
When I started in Java, I found Sun's tutorials to be helpful. And in preparing for the SCJP exam, I used Dan Chisholm's practice exams.