The commentary on this movie is ridiculous and amazing. A lot of it is Arnold talking about how huge he is and John Milius groaning in ecstasy over Sandahl Bergman (which they highlight here). The whole thing is just thoroughly entertaining. It's one of the few commentaries that I've made it through the whole movie with.
Fear and Loathing in Las Vegas - Criterion collection edition: Hunter S Thompson going batshit loco
The Thing: Again, Carpenter and Russell always have a bunch of great anecdotes
Any Werner Herzog commentary: Do i even need to explain?
With the age of the digital download pretty much here, I'm going to miss commentaries. This is easily one of the best, if for no other reason then how hard Arnold laughs at the guy getting kicked in the balls. "He was laughing, and then he wasn't. HAHAHAHAHAHAHAHAHAHAHAHAHA!"