After Effects does this to the extent that you can control an objects size, position etc from an audio track, Haven't tried this myself as it's fairly complex to setup but if you wanted unlimited possibilities along with a steep learning curve that's one answer.

The latest vision mixers from Edirol seem to have heaps of such effects built in if doing things in realtime appeals.

Simply capturing any one of the visualisers off the screen is a very cheap solution.

There is a VST plug around that will write an envelope that can then be used to control a few things in Vegas. This is fairly limited in its application.

Bob.