The one that has been played more times than any other.

I would have to say "Scrubs" (S1-S4) has been played at least 3-4 times and that is a lot of DVD. I have to watch them all in sequence when a new season is coming out. Now S6 and I am almost done with S5.

Definitely my most played and valued.

Apollo 13 for me.

My Babylon 5 sets. I've watched that series more times than I'd care to count. For movies it's probably between the Almost Famous Bootleg Cut or the Lord of the Rings EEs.

Dead Like Me (both seasons) - 5 times with some episodes more
Firefly - Viewed so many times by myself and friends that I need to get a new copy of it
Sin City - Same as above
a couple others that aren't coming to mind.

Boiler Room
Firefly
Rock Criterion Collection
The Matrix
Simpsons Seasons 2-5

Freaks and Geeks

Arrested Development

I watch those DVDs constantly.

Individual DVD? Rudy. I think I've watched it at least 12 times.

I've watched Firefly at least 5 times and loaned it out 3 more times for a total of 8

The Shield I've rewatched from the beginning every time a new season comes out, plus did a Marathon with friends so that makes 6 viewings for me and I've loaned them out to at least 6 other deputies.

The most mileage? Invaders from Mars.

I haven't watched it yet, but it came from Mars man.

Tom Goes To The Mayor, The Wire 1-3, Knife In The Water and The Dreamers all make an apperence in my dvd player at least once a week.

easily Arrested Development season 1 and probably Fight Club and Road Trip as far as movies go

Cars

TV:
Stargate SG1 - S1-4
Xena WP - S2

Movies (is this weird?):
1776

Extras S2 (US version)
and, I'm not sure why, but X3 The Last Stand

dawn of the dead
blue velvet
the thing
family guy vol. 1
vanilla sky
fight club
jaws

The original Outer Limits series has probably been my most-watched DVD set. I just do not get sick of those.

Mostly TV on DVD:

- Various Simpsons seasons
- Aqua Teen Hunger Force
- The Office
- Arrested Development (until they were stolen)
- Freaks & Geeks

I also watched Borat five times with different crowds the first two weeks it was out on DVD.

Sports Night complete series
The Wire seasons 1 and 2
Battlestar Galactica season 1

The Big Lebowski or Dazed and Confused

Reservoir Dogs

Due to my daughter, I have more than gotten my money's worth out of these DVDs (and these are just the tip of the iceberg):

The Iron Giant
Finding Nemo
Monsters, Inc.
Toy Story 1 & 2
The Incredibles
Curious George
Millions

I've probably gotten the most mileage out of:

The Goonies
LotR: FotR - EE
The Big Lebowski
Rushmore
Batman Begins

W/ the wife:

Beautiful Girls
Notting Hill
Sliding Doors
The Bourne Identity

any action movie in my collection

Without a doubt

Schoolhouse Rock
The Many Adventures of Winnie the Pooh
Bram Stoker's Dracula (Superbit)
The Rock
Independence Day
Eyes Wide Shut/A Clockwork Orange/Full Metal Jacket/The Shining (the hubby is a Kubrick supporter)
Air Force One
X-Files (in varying degrees)
Bond - all movies (and I know I'll quadruple dip if any aspect of these DVDs is improved upon)
Star Trek: Deep Space Nine
Silence of the Lambs and extra features on the Criterion disc
Seinfeld series
Freaks & Geeks (I've watched these far too many times - each episode is fresh each time)
The Up Series - my all-time favorite documentary series and I LOVE documentaries

I've been watching a lot of Hitchcock lately; it's as if I just discovered these movies and I've seen most of them more than twice

Serial Experiments Lain
My So-Called Life
Freaks and Geeks
Wonderfalls
Firefly

For some reason, these short one season shows hold the most rewatchablity for me. I know I can start it, watch a few episodes in a row here and there and be done in a few days. Not as much commitment as if I wanted to rewatch something longer like Buffy or Babylon 5.

I've watched Freaks & Geeks, Undeclared and the LOTR EE trilogy at least 8 times each.