Many have suggested Rockplayer. The first time I installed it I had some issues with playback. But I tried installing it again a few days later and it works awesome now.
Mobo looks like a decent app but is twice the size of mVideoPlayer. On these tablets size is everything if you have allot of apps. My vote is still mVideoPlayer. I think the relatively few bad reviews on Market are due to hardware. It works great on the Kyros with everything I throw at it like avi and mp4. It is also free.
What I do to watch videos(and this should work with movies too), is I go into gallery, and it will show categories like pictures. One of them will be videos. All videos on the nand and SD card will be shown there.
QuickPic does the same as gallery, Mobo Player does both audio and video in 3D picture view and Meridian Player prior one I don't like the current version. Does both video and music. All Search the Nand or Sdcard.