Taking a cue from Bonnie's comments on another thread, I thought it would behoove me to mention a few (maybe forgotten) DVDs that have some really cool extras.
1. Shaun Of The Dead. Sure, by now we've all seen of it a dozen times, BUT the DVD has two separate commentaries by both the director/writers AND the cast - and both are hilarious! Also, there is a 'graphic novel' plot hole extra that fills in some questions. Plus, 25 deleted and/or longer scenes.
2. Dawn of the Dead (2004). 3 years before '300', Zack Snyder gave us this little remake that (dare I say) is better than the original. He has a commentary track as well (with the writer) and the best part is, they recorded it WAY before it the theaters, and at one point they both mention how they think the film will tank and will be the end of their careers - whoops!. Also, there is one extra devoted completely to the guy that was stranded on the gun shop building - that is pretty cool.
3. Joyride. I hate Paul Walker. But the guy that wrote 'Lost' and 'Alias' penned this flick, and I gotta say, I dig it. What's more, there is a 30 minute alternate ending! It's a like a completely different movie! Also, the commentary with Steve Zahn left me in stiches.
4. Once Upon A Time In The West. OK, this one is dated and may just be for western fans, but the commentary done by some great filmmakers like John Carpenter and Bernado Berdalucci grant this another viewing - one points out a GAPING plot hole that I never noticed before - dammit!
One of my favorite DVD commentaries has got to be Conan the Barbarian... Arnold's commentary is friggin hilarious, and the outtakes especially the one of him running from the dogs when he escapes slavery is one of the funniest things I've seen in my life.
Tombstone, Boogie Nights, Fight Club, Magnolia, Raging Bull, The Nightmare Before Christmas and Shawshank all have very nice editions out. The extended editions of Lord of the Rings also go without saying.
The special anniversary version of the Atlantis cartoon that Disney did. I know, I know, I'm usually not a big Disney fan but listening to the commentary and how they creativly designed the underworld and culture I thought was very interesting.