In the advanced search tab, there is already a Reset button that will reset all fields which is nice. However, I'm interested in implementing something like emule's search windows. Emule opens up an independent search window for each search you run with the ability to close any of them at any time. There is also an option to clear all the search windows at once, which is convienient when people are running numerous searches.
Though its just a small thing, I think it would make searching a bit easier. Plus, the anidb's advanced search has filters which is super great