Movies2iPhone can convert any movie to your iPhone, iPod and iPad the easy way. The iPhone is a wonderful device. However when it comes to play videos it turns out to be very picky.
Indeed, the iPhone only accepts to play movies encoded in a very specific format: the so called mp4 format.

Movies2iPhone converts any video (Divx, Xvid, avi, mpeg, wmv, asf, mov, vob, flv (flash), 3gp, mkv, etc...) to a format optimized for your iPhone, iPod or iPad.

It is extremely easy to use, free for non-commercial use and does NOT require your iPhone/iPod/iPad to be "JailBroken".

Movies2iPhone currently runs under Windows Xp, Vista, Seven (32 & 64 bits) and Mac OSX Leopard (10.5) and Snow Leopard (10.6).

Movies2iPhone uses FFmpeg.
FFmpeg is a fantastic command line program that can record, convert and stream digital audio and video in a wide range of formats.
In particular, it can convert most video format in the mp4 format. A video format compatible with the iPhone, iPod and iPad.
But since it is command line driven and uses an enormous amount of configuration parameters, it is prety hard to use.

Movies2iPhone acts as a front end for FFmpeg, it creates an easy to use graphical interface for FFmpeg, dedictated to one single task: Converting videos to the iPhone/iPod/iPad format.

The license of this software is Freeware, you can free download and free use this video converter software.