You can also go to the site virtualdub.org, and check the links page for a *Bunch* more, search the web etc...
RE: are they any good, most are done by some pretty heavy coders, optimized to perform fast, and often target wants/needs not adressed by commercial publishers. There are a few oddballs, but by and large the filters are excellant.
I've decided that I don't have the time or energy to hunt down and maintain a list of all the current video filters available for VirtualDub, so I've appointed Donald Graft as honorary filter website maintainer. You can find his own filters, and a comprehensive list of other third-party filters, at: