I've used ACT media player and that is very good. But I just recently found out that Meridian (which I originally got just for music) plays video files and can also load subtitles which is a big plus for me. So far it's the only one I know of that does that so I would rate is the best on that alone. The developer has been updating a lot recently and it's really gotten good now.
It does music and movies, and even has a file browser. I really haven' been able to find a better music/video player so far.