You can find many free filters on the Internet to add to your VirtualDub filter library. The VirtualDub homepage has a filter section that contains some extra filters that are not shipped with VirtualDub. Check http://www.virtualdub.org/virtualdub_filters/.
Another shrine for VirtualDub and AviSynth filters is Donald Graft’s homepage at http://neuron2.net/.
The installation process goes from easy to non-existent for filters. Once you download the filter, usually contained in a ZIP file, follow this process: