7. Robert Downey Jr. In Character - Tropic Thunder

Though not everybody is in character in this commentary, Robert Downey Jr. is so committed to his work that it doesn't matter in the slightest, and of course, it's a brilliant recall of Sgt. Lincoln Osiris' line in Tropic Thunder - "I don't drop character 'til I've done the DVD commentary."

This is a commentary that really lets fans of the movie have their cake and eat it; first of all, director and star Ben Stiller actually provides some pretty nifty facts about the ins-and-outs of the production, while Jack Black occasionally chimes in with a funny tidbit here and there.

Then there's Downey Jr, who continues to act in character as Kirk Lazarus playing Osiris, and appears to have concocted a series of amusing set stories that prove just how much effort he and the others must have put into assembling the whole thing.

Hearing Downey switching between his Osiris voice and his Australian Lazarus accent is an absolute riot in of itself; in terms of commentary that has a direct interplay with the film, few can even dream of measuring up to this.