DK Finder 188.8.131.52
We have seen index-based file searching tools before - but this one is really fast and smart.
Once you have your index, results appear in about half a second, then can be narrowed further in realtime. Finder has az optimized reindexing technique which can update your index in a few seconds, and many features for managing your result lists. Can be hidden to system tray, has easy-to-remember keyboard shortcuts for nearly everything, and has a separate reindexer process that can run silently in the background whenever you want it to, disturbing nothing else you work on. (Not even your searches - they can be done paralelly.)
Finder is fairly configurable, has many options and has a relatively small footprint when resident. You just start it, then forget about it - and whenever you need a file, it will be there in a sec.