I wanted to see what all the hype was about, so I broke down and upgraded my iPod to a new black 60Gb video model last week. I moved over the iTunes videos I'd bought but soon after looked around for programs to help move existing movie files onto the iPod.
From the Handbrake lite site, I quickly found iSquint, for converting video on your hard drive into iPod format. The application can convert virtually any video format and in all the things I've thrown at it, everything has worked great. It's pretty amazing actually -- no matter the bitrate of audio, the compression format of video, no matter the source of the video... everything ends up in a compatible format. So that means if you've got a few random bittorrent episodes of a TV show in all sorts of crazy formats, chances are it'll work just fine in iSquint.
After using it for a week or two, about the only thing I'd suggest is that the default quality settings sometimes degrade the audio and video slightly too much, but the fix is easy: I just up the quality one notch higher on the sliders. Conversion is fairly fast on my 2Ghz G5 iMac, with video recompression going about 2x real-time (it takes maybe a half hour to convert 1 hour of video). Whenever I want to use iSquint, I let it do its thing when I go to bed, so it's not really in my way or dragging down my typical activities.
If you have a mac and a video iPod and were wondering how best to convert existing movie files you have on your hard drive, iSquint is the easiest and most straightforward option I've found.
For PC Users: word on the street is Videora works pretty much the same as a great video converter.