Please see the Objects by Design
forum thread which discusses the interesting UML tool J2U.
I do disagree, however, about the utility of static class diagrams. It is much, much quicker to get an overview of the software by looking at the class diagrams than looking at the source.
Conversely, looking at some reverse-engineered sequence diagrams can take a while to sort out, especially without hyperlinks from the objects on the sequence diagram to the class diagrams for these objects. See some of the reverse-engineered sequence diagrams produced by J2U in the thread above for examples.