I wanted to get some movies onto my iphone without itunes, largely because I run linux at home. There are various ways proposed online - the most common being to mount the iphone as a storage device - but there's a very, very easy way: VLC.

1. Download VLC from the iOS app store
2. Get the device onto the same wifi network as your computer
3. Open up VLC on the device, click the menu icon, and click wifi sharing.
4. On the computer, use a browser to navigate to the shown IP address.
5. Click the upload button, upload the videos you want.

That's it. Super easy, took a few minutes. Works on any major OS!