I actually don't listen to commentaries that often. Except ours.

Which makes me unqualified and narcissistic. Pa-pow!

My favorite commentary is Fight Club's with Fincher, Norton and Pitt.

I listen to pretty much every commentary track on every disk I own. I always enjoy the Simpsons commentaries, atho the Futurama ones are even more fun, and I've particularly enjoyed Edgar Wright and Milla Jovovich. Of the scholar types, I quite like Eddie Muller's commentaries for classic film noir. I like Roger Ebert, but it really burned me that he got the "General Degaulle/Weygand" issue wrong on Casablanca.

The absolute best commentators are Simon Pegg and Edgar Wright.  Their commentaries for Shaun and Fuzz have me in absolute stitches every time I listen to them (which pre-DIF was... often, and we'll leave it at that). 

Kev Smith and crew are always fun to listen to, the Clerks II cast commentary is very funny.

Carpenter and Russell do a pretty good one for Big Trouble in Little China, IIRC.

Yeah, Dorkman. I agree on the "Mouth of Madness" track. I watched the film recently based on the suggestion I heard during a DIF commentary. I'm not sure if you referenced it or if it was Teague. But, someone suggested it for lovers of H.P. Lovecraft and "unseen" evil.
Good film but the track was weak. Especially given Carpenter's track record. His sit-downs with Kurt Russell are gold! Listen to "The Thing" or "Escape from New York." And, as mentioned above, Big trouble in Little China.
Only time Mel Brooks "schtupped" me was the special anniversary edition of "Blazing Saddles." I swear he stops talking after the first 15 minutes. Or the mike was not on....

The commentaries on the Venture Bros DVDs are amazing. They tend to have almost nothing to do with the episodes, but you get a sense of what it's like when the two driving creative personalities behind the show are locked together for months at a time producing one of the best things on television. They only did a couple for the first season, but the response was so overwhelmingly positive that they've done a commentary for every episode on every season since. I get the episodes on iTunes, but buy the discs afterwards particularly for their tracks.

The Kingdom of Heaven Director's Cut DVD has one that flips between the executive producer, vfx supervisor, and the 1st AD. Never heard a first AD on a commentary before, but that should happen more often. Had a bunch of great stories from production, and didn't have to worry about offending anybody since he wasn't up near the line. Also didn't mind talking shit about his own work, like in scenes where all the extras are walking at the same speed or something.

Root canal is considerably funnier than that movie.

That's pretty much how it is on all the Milla Jovovich movies I've seen/listened to the commentary, regardless of whether the movie did what it set out to do (Resident Evil) or not (Resident Evil 2). I seem to recall the one on Ultraviolet being boring, tho. Maybe she's not on that one. Even if she was, there's no opportunity in that movie for her to shout, "Wait! Look! There's my boobies!"