Yeah, I would go with these. And they are all available on DVD, too.
Except Pumaman, which isn't.
Once again, let me disagree with the other suggestions. Our favorite episodes may not work for newbies. I certainly wouldn't inflict Manos on someone who's not familiar with the show. I'd suggest either one of the shorts sets (which may be out of print these days) or a film with a stronger narrative sense than most MST3k films as a film that is somewhat enjoyable to watch by itself often makes the best entry riff. Cave Dwellers or Radar Secret Service would probably fit the bill best. Maybe Agent from HARM, Danger Death Ray! or Riding with Death too.
Don't forget, almost every short is on Youtube these days. Thanks Jim for not enforcing your copyrights!