This work on the OPAL project uses curves instead of traditional poly-lines to alleviate some of the effects of the 'crossing problem' - i.e. following lines through dense knots or cross-overs.
The link below is to a demo version of this visualisation. It is a java web start file that will launch and ask for permission to run. Uses Java Webstart & Java 1.5, tested on IE6 and Firefox.