I have the 1-disc Wall-E with a commentary by Andrew Stanton but a few of the reviews I've seen say the blu-ray has an enhanced version of this commentary plus two other new enhanced commentaries (with branching and extra video bits). I just got done listening to the commentary on my DVD and it's not negative at all so I'd imagine the blu-ray has the more interesting commentary.
As for ones I like, come to think of it this Wall-e one I just watched was pretty informative about where the story ideas came from and how everything developed. As always, Pixar gives good dvd.
I'll second everyone who said the LOTR, Once Upon A Time In Mexico, Resident Evil, The Thing, and Big Trouble In Little China commentaries were all good ones.
I really like all the commentaries on the special edition Sin City dvd where Robert Rodriguez does his thing and has Bruce Willis, Quentin Tarantino and a few other people pop by at the relevant points. Quentin is pretty hilarious on his bit, he sounds like he was...on something.
Fight Club has a good one with David Fincher, Ed Norton, Brad Pitt and Helena Bonham Carter (although it's very obvious she was recorded separately and kinda messes with the flow of things in some spots, overall it's a good track). The Chuck Palahniuk/Jim Uhls (book writer/screenwriter) commentary track on that one is also pretty entertaining.
Carrot Top's commentary on The Rules Of Attraction is a bit out there but I love it anyway. I love his reaction when the movie finally gets serious (or about as close to serious as it ever gets).
The newest special edition release of Spaced has a lot of great commentaries on different episodes, including all of the original ones plus some new ones with people like Kevin Smith and Quentin Tarantino guesting. All great.