Not sure if the logging framework is included, but java.util.logging.LogManager is a singleton, I believe, and java.util.logging.Logger is instance controlled. java.awt.Toolkit is also singleton. Those are the only examples I can think of right now.
java.awt.Toolkit is an abstract baseclass but it is most definitifely not a singleton.
Ok my fault. Its sort of a mingleton. I think you could argue about that too because a singleton or derivates must always return the same Object but you can change the returned Object of the Toolkit.getDefaultToolkit method.