Save YouTube Videos to iPod (Mac)

It's called TubeTV, and it's free for the Mac.

Open TubeTV. Click on "Grab URL". YouTube will open in the application. When you find a video you'd like to download, click on "Save".

In iTunes, click on "File/Import/" and select the video. Then right click on the movie you just imported, and select "Convert Selection for iPod/AppleTV".