RapidSearch (@willwood) also has:
RapidSearchGo (uses DuckDuckGo)
RapidSearch (uses Google)
RapidSearchLive(build your own Flatefile Index based on Metadata)
and the mentioned RapidSearchPro (builds a MySQL database of all content).
The Google and DuckDucvkGo versions you are dependant on when and what the search engines index. The Live and Pro you build the indexes.