Fight Club has 2 very good commentaries.
1. is brad pitt, edward norton, david fincher, and helena bonham carter
2. david fincher by himself, he talks a lot about the process of the film being made and taught me a lot about it.
Requiem For A Dream also has 2 very good commentaries
1.Darren Aronofsky talks about the novel and how he came about the film and the characters and the film itself, its defintly worth a listen
2.The Director Of Photography gives a very very technical commentary and anybody who wants to work with cameras needs to listen to this.
Good Will Hunting's commentary featuring Matt Damon, Ben Affleck, & Gus Van Sant is entertaining and inspiring and thoughtful.
The worst commentary belongs to the Matrix, the horror, the horror.