I use an Asus EEE Pad Transformer as my “main” Android tablet. However — I found that I was unable to view MPEG-4 (AKA MP4 or H.264) videos. That is when I discovered the free MX Video Player on the Android Market after trying a couple of different video player apps. If you do not desire to see the advert banner in the free version, you can opt to try the MX Video Player Pro which does not use advertisements.
Regardless of the version chosen, after installation open the app so that it may determine the compatible codec to install to match your tablet CPU and video hardware. You will once again be directed to the Android Market to download the free codec. For the Asus EEE Transformer the ARMv7 codec (at the time of this writing) is the codec MX Video Player selected as the best match for the tablet and video chipset.
Upon installation of the video codec, open the player once again, tap the OK button after reading the contents of the What’s new in version x.x dialog that appears one time upon a new installation or version upgrade. Navigate further by tapping the Movies folder and lastly select the MP4 video (if present) for viewing.
Your selected MP4/H.264 video will begin playing. You can tap the screen at any time to make standard video controls visible at the bottom of the screen.
Disclaimer: I am not associated or employed by any company producing software or hardware reviewed on this site.