I've always found Adobe Bridge to be good for organizing, tagging, and searching through large amounts of videos. Bridge comes with almost any Adobe product such as After Effects, the current Photoshop Elements, etc. When you find a clip within Bridge that you like, you can simply select it, right-click, and go to Open With > FCE4 to import it into FCE for editing.
I'm sure there are other programs or methods that might be more appropriate for a normal FCE workflow, but that was my initial thought.