Small and pretty simple but powerful in the same way - JW FLV Media Player
Very easy to use, supports playback of any format the Adobe Flash Player can handle (FLV, MP4, MP3, AAC, JPG, PNG and GIF). It also supports RTMP, HTTP, live streaming, various playlists formats, a wide range of settings and an extensive javascript API.
Must have tool if you want to play online video on your site.