Javasoft's homepage. Get the JDK here, as well as enough information to keep you busy for weeks.
IBM developerWorks page for Java. Information and resources relating to Java technology.
Blackdown's website. Get the JDK 1.3.0 for Linux as well as some other useful Java applications.
Apple's Java page. Get the MRJ 2.2.3 as well as Macintosh-specific Java information.
The Web Developer's Virtual Library contains information on a variety of topics ranging from Java to website design to databases and more.
Nice resource for developers. Articles, tools, forums, etc.