This is the second open source application review that I've done, but it really should have been the first. I could probably live without talking to other people (Adium), but I'm not sure I could survive long flights without the occasional movie. Handbrake covers this fundamental human need.
If you're not currently using the open-source Handbrake application, your life is woefully incomplete. Handbrake is one of the applications that you will continue to use when you die. Angels are using it, even as I type, to rip their DVDs to their hard-drives so that they can save battery life on long trips (to Redmond, most likely :-).