If you're taking suggestions Patrick (and since you're obviously not doing the Rifftrax thing of only going after movies that are DVD best-sellers):
-the new batch of 'anti-hero' hero movies ("Kick-Ass," "Super," etc.) that have hit the market. They're prime 'meta-on-meta' material commentary for people like you that know the superhero movies that inspired a new generation of filmmakers to make them (i.e. the commercial blockbuster necessity to have a PG-13 rating neutered the big studio superhero movies' ability to go as dark as they could have, leading to the over-the-top blodshed seen "Super" and such).
-"The Dark Knight" because (a) everybody owns it, (b) everybody has an opinion about it, (c) the 'down time' in-between scenes could be used to talk about the actors (i.e. how Gary Oldman is cast against type as Gordon), (d) the current version doesn't have a DVD commentary and (e) it'd be a nice tie-in with the building hype for next year's sequel.
-anything "cult" that has sold on DVD (not necessarily in the bazillions but sold well)
that also happens to be available for streaming on Netflix, Hulu, Amazon Prime (combination of either), etc. so that those that want to listen to the commentary but don't have the DVD have the option to stream the flick. Examples (of DVD ever-green "cult" flicks, not stuff available for streaming): Romero's "Dawn of the Dead," Carpenter's "The Thing," "Grease/Saturday Night Fever," etc.;
-Stuart Gordon flicks are a commentary gold mine, IMHO: "From Beyond," "Re-Animator," "Dagon," etc. They're borderline silly at times but have a strong backbone that supports both mocking and complementary comments. Personally I'd love to hear a commentary from you guys on Gordon's "Dolls" but I don't think enough people have seen it (or own the DVD) to make the commentary worth your while. A guy can dream;
-The first "Hellraiser" movie. It's a good flick that has, sadly, a lame commentary in which Clive Barker comes across as someone that doesn't want to be there;
-A David Cronenberg movie, take your pick. The man's had a fascinating career and his themes repeat enough throughout his work that doing commentary on one is like doing commentary on all of them. Personal choices: "The Fly" (my favorite movie of all time, and one of
TIME Magazine's 100 Best Movies of All Time), "eXistenz," "Videodrome," "Dead Ringers," etc.