Back when I was working at the video store, there were a few staples that we always played in the store. The main criteria, of course, was that the movies had to be entertaining. Perhaps my favorite was Conan the Barbarian with the John "Red 'Motherfucking' Dawn" Milius and Arnold Schwarzenegger commentary on. For those who have not listened to this commentary track, it is truly a thing of beauty. Apparently, at the time, Arnold was a special needs student who had never seen the movie until he sat down to do the commentary, and thus felt the need to give a dumbed down play by play of everything that happened on screen. His thoughts consisted of such nuggets as, "And here is me with the sword. And here I am running...and I'm running...and I'm running."
Although I would love to post the entire thing here, I can not find it anywhere. I did, however, find this clip, which someone was nice enough to make, of some of Arnold's choicest pearls of wisdom. This video does not even begin to convey the awesomeness of the commentary track as a whole, but it is well worth a watch.