Mplayer is a media player for the iPhone that supports a variety of formats like mpeg4, wmv, mp3, acc, wma, real-media, h.264, etc. The files have to be placed using iPhone Browser or FTP to “/private/var/media” on your iPhone.
The App works great and is our choice for the Video Player on the iPhone.
Cydia is an Installer alternative, that Installs on Jailbroken iPhone 2.x… Info here