I only know about IndieVolume. It crashes often for me also on a lot of webpages. Kind of defeats the purpose, but the author is constantly removing bugs, so i can't really complain. I think it's difficult to make it really stable because everyone's internet programs are so wildly different, especially with Firefox and all the plugins and stuff. FOr an audio program to intercept and work smoothly with everything must be difficult.
PS Go to the new Milk website for whitegoldiswhitegold.com It is SO LOUD, even on my very low volume settings. Geez, it's insane. I wish there was an application like TV's have now where the volume adjusts so it never goes over a certain volume.