Web site YouTube Fast Search dynamically searches for new YouTube videos and creates playlists while a video is playing. If you've got a list of videos you know you want to queue up after the current one finishes, YouTube Fast Search will do the trick. Aside from the dynamic search, it also all happens through a really nice drag-and-drop interface. It could still use some work on playback controls, though, which were buggy for me.
YouTube Fast Search [via Google Operating System]