Mac OS X: If you need to convert a video for your iPod, a DVD or even just rip the audio out of a movie, free app Media Converter will do it with just a quick drag-and-drop.
Previously mentioned Handbrake is usually our go-to video converting program, but if you don't need to use all of its advanced features, it doesn't get any simpler than Media Converter. In fact, it's especially good for your DVD-burning, iPod-weilding relatives and friends that are too intimidated by Handbrake's advanced interface: you just pick a file format from the dropdown menu, drag in a video file, and you're done. It will immediately start converting the file for you and alert you when it's finished. Literally, the only way it could be simpler was if it read your mind.