I'll agree with the assessment of the Family Guy commentary tracks. Way too dull.

Simpsons season 1 also sucked. Way too many "look how cool we are" statements for me.

I also have to mention Chris Nolan's commentary for Memento. Maybe he gave great background on the movie... we'll never know, because he mumbles the entire time.

Guy Ritchie's commentary (along with his producer) for Snatch was pretty lame: "Uhhh...uhhhh...mumble...unhhh..." After about fifteen minutes, he actually said, "Well the guys in suits just came in and told us we're not doing it right. They want us to talk more about making the movie and uhhh...uhhh...mumble..." I guess it didn't occur to them to start the recording over and do it right!

Ed Bishop's commentary on one of the episodes from the UFO boxset was pretty bad (he played the lead, Commander Straker). Bishop seems to be getting up there in years, and it appeared that he just didn't "get" what commentaries were supposed to be about. He gave lots of insights like, "There's Michael Billington. He's a fine actor, fine actor...There's Gabrielle Drake, a great gal! Joe Blow did the model work, he's very good. There's George Sewell, what a nice guy..." I kinda felt sorry for Bishop; somebody should have explained to him what this commentary thing was all about.

I often listen to commentaries and one of the worst ones I ever listened to is the commentary for the 35th anniversary for Planet of the Apes. The actors seemed bored and the pauses were way too long.

My favorite audio commentaries are the ones with James Cameron (T2:EE, Solaris, Aliens) Terry Gilliam's commentaries (12 Monkeys especailly) are also fun to listen to. I also like Ridley Scott (Hannibal especailly)

Galaxy Quest: that alien commentary. Sucked. Couldn't understand one word!

i have never been annoyed with anyone on a commentary track until recently, hattie on the red dwarf s3-4 commentaries, everytime she laughed it made my ears bleed

A lot of people are giving Friedkin a hard time but definitely give his commentary for To Live And Die In L.A. a chance. He is very informative and though some of it is repetitive if you watched the documentary, it still is pretty good. You do have to gloss over a few parts where he becomes a little too self-appreciative as well but as others have said, his voice is mesmerizing.

In one of the Hitchcock disks in Wrong Men & Notorious Women, post-feminist deconstructionist scholar Marian Keane has decided that the movie is a precursor to NxNW and everything on the screen (and a lot that isn't even there) is something that will be done better in another movie.

Any Babylon 5 commentary with Jerry Doyle. Great actor, I love his character, but I cannot stand his pointless ramblings about how different they all look and how much hair he has lost.

Ridley Scott for Gladiator! I was worried I'd be the first one saying it. He just goes on and on about what's happening on screen. To his credit, he does say a few bits of interesting trivia but that's about it. A worst one is the one from The Nest, a French action flick. The director says EXACTLY what's happening on screen and only offers 2 bits of information about the actual production and costumes. The Intacto commentary was kind of the same, although in this one you could tell the director was really passionate about his movie.

Okay, commentaries are my favorite extras and I ALWAYS finish them. I always listen to them also.

T3 - no the commentary doesn't pick up halfway through but I didn't find it too boring. Just your average commentary.
McTiernan does have a dull voice but he does give out a lot of interesting information. The Predator commentary is a good example.
Okay, I love Criterion, but many of their spliced track are kind of disappointing. I thought the Hard Boiled and Sullivan's Travels tracks would be better.
Matrix track - probably the worst I've ever heard. Just awful.
The Full Frontal and Lawnmower Man tracks were not terrible but they got long after a while.
ID4 - I think it's the first time I heard a technical track that had more insight, anectdotes and information into the making of the movie than a director/producer track. The technical track is good, the Roland Emmerich/Dean Devlin track is bad.
Triumph of the Will - some university professor who narrates what's happening on screen. I find this especially annoying because this isn't an experimental film or anything, it's, like, a documentary. If you don't understand what's going on, you pretty thick. He does say a few comments about other things, for a big part of the track he tells you what you're seeing.

Those are all I can think of for now.

Does it seem to anyone else that generally the weakest commentaries tend to be solo efforts? I've often found them more interesting when there are two or even three people bouncing comments off each other.

Not if it's Bruce Campbell or Joe Bob Briggs!

Just to echo what a lot of people have already said, plus adding a few more...

The Best: David Fincher, Kevin Smith, Ridley Scott, James Cameron, Terry Gilliam

The Worst: John McTiernan, William Friedkin, The Coen Bros., Richard Donner, Rob Reiner

Hit or Miss: John Carpenter, Steven Soderbergh, Sam Raimi, Paul Verhoven, Jan De Bont

Criterion's laserdisc editions of Adventures of Baron Munchausen and Fisher King have fantastic commentaries from Gilliam, oh how I wish Criterion could reacquire these from Columbia/TriStar films and port the great supplements to DVD. (sigh)

This list won't be complete until you add the Farrelly Brothers, absolutely the worst commentaries I have ever heard (though if you were their neighbor's cousin's friend and appeared in the background for one shot, I'm sure it made your day).

Any one by the Farrelly Brothers. Annoying roll calls.

American Beauty is the only one that sticks out to me.

Well, I've heard so many bad things about their commentaries, I haven't bothered listening to a single one! I'm not a big fan of theirs anyway.

The commentary on A Guy Thing was extremely annoying. I'm not sure who it was on the commentary who was so annoying. If it was Selma Blair or Julia Stiles. But it seemed that all the others would ignore this person.

Also Tim Burton's commentary on Sleeping Hollow was extremely boring.

wow, am i the first to mention the peice of crap commenatary with Slater and Arquette on true romance. they obviously haven't seen the movie in a long time

Best Commentary: John Carpenter's They Live, with JC and Rowdy Roddy Piper!
Worst Commentary: John Carpenter's Assault on Precinct 13, with JC

The worst I've ever heard in my life are:

Tim Burton on Planet of the Apes: Good heavens I couldn't get 5 minutes into it. So damn boring.

William Friedkin on The Exorcist VYNSB: Already been mentioned. He basically narrates the movie. His commentary on the original release was better.

Robert Zemekis on Cast Away: BORING. Had no interest in what he was saying, he was just so boring.

Director on Blair Witch 2: What a prick this guy was. Blamed everyone but himself for how bad his movie was.

Brendan Fraser on The Mummy: Geez, this guy sounded so stoned I was getting a contact high just from his voice. Boring. "uh...hahaha.....uh...erm.....hahaha"

Sam Raimi and others on Spider-Man: Very disappointing. They had nothing to say that interested me in the making of the movie. Bland and boring. Commentary on Spider-Man 2 was a lot better.

John Frankenheimer on DC of Reindeer Games: "zzzzzz...huwha..what? Oh yeah, this scene is a lot sexier in this vers-zzzzzzzzzzzzzz."

The Home Movies: Season 1 commentaries are pretty annoying to me. The background volume seemed to loud at times. It was kind of hard to understand what Jon Benjamin was saying.

John Boorman lives up to his name on the Excalibur audio track. He's boring.

John McTiernan is a bore-fest.

Irvin Kershner's narration on "The Empire Strikes Back" is the worst. no insights from an intelligent perspective, preferring to describe the action on-screen as though he were talking to an 8-year-old, and punctuating everything with variations on, "and that's the oldest gag in the book."