Here’s the formats I’ve got so far:
VHS:
Toy Story
A Bug’s Life
Toy Story 2
Monsters, Inc.
Finding Nemo
DVDs:
The Incredibles
Cars
Ratatouille
WALL-E
Up
Toy Story 3
Cars 2
I also have Pixar Short Films Collection: Volume 1 on DVD, and I’m thinking about getting Cars Toon: Mater’s Tall Tales also on DVD.
Here’s my list.
VHS
Toy Story
Toy Story 2
Finding Nemo
DVD
Toy Story
A Bug’s Life
Toy Story 2
Monsters Inc
Finding Nemo
The Incredibles
Cars
Up
Toy Story 3
Cars 2
Blu-Ray
Cars
Here’s my updated one:
VHS:
Toy Story 2
DVD:
Toy Story
A Bug’s Life
Toy Story 2
Monsters Inc.
Finding Nemo
The Incredibles
Cars
Ratatouille
WALL-E
Up
Toy Story 3
Cars 2
Pixar Short’s Film Collection Vol 1
Blu-Ray:
Toy Story
A Bug’s Life
Toy Story 2
Monsters Inc.
The Incredibles
Cars
Ratatouille
WALL-E
Up
Toy Story 3
Cars 2
Now if only they’d release Finding Nemo on Blu-Ray (hopefully they actually do it this time).
My DVD list is the same. It’s interesting to note that all of them from Toy Story to The Incredibles (as well as Ratatouille and WALL-E) are Region 2 collector’s editions with 2 Discs. I also used to own VHS tapes of the movies.
A Bug’s Life and Monsters Inc’s collector’s editions were out of print. Monsters Inc was easier to find though finding A Bug’s Life was tough but in the end it worth it. The picture quality is incredible (perhaps better than the standard DVD) and the special features (including the commentary) are a must.
I’ll also say that the standard 1-Disc DVD of Monsters Inc in the UK has the film in 4:3 fullscreen format for some reason, but the collector’s edition has the original 16:9 widescreen transfer of the film and many bonus features which make me favour it over the standard edition.
So that makes it like this.
VHS:
Toy Story
A Bug’s Life
Toy Story 2
DVD:
Toy Story (2 Discs)
A Bug’s Life (2 Discs)
Toy Story 2 (2 Discs)
Monsters Inc (2 Discs)
Finding Nemo (2 Discs)
The Incredibles (2 Discs)
Cars (1 Disc)
Ratatouille (2 Discs)
WALL-E (2 Discs)
Up (1 Disc)
Toy Story 3 (1 Disc)
Cars 2 (1 Disc)
Pixar Short Films Collection: Volume 1 (1 Disc)
For years, I was fine with DVDs; so the first Pixar films I owned were all on that format (Monsters Inc, Finding Nemo, Ratatouille, WALL-E, and Cars). But then one day in 2009 I realized that the Blu-Rays had so much more bonus material (and I’d already begun to notice the lack of bonus features on Ratatouille and Cars; thank goodness I found the Deluxe WALL-E DVD), and I decided that I was going to start getting the Blu-Rays for a change. Thus, the rest of my Pixar films are all on Blu-Ray (A Bug’s Life, Up, Monsters Inc, Toy Story, Toy Story 2, Mater’s Tall Tales, The Incredibles, and Cars 2). And as a note, these lists were how I got them in order. My first Pixar film was MI, and I watched it so much that the DVD didn’t hold up, so in 2010 I decided it was about time to get the Blu-Ray edition. Now, I plan to replace Cars and Ratatouille to get the bonus features I’m craving, but I don’t know about the others. I’m such a behind-the-scenes geek 
Now, I just need the Pixar shorts and the Buzz Lightyear movie!
I bet they look fantastic in Blu-Ray. I’ve not really cared much for it, I personally prefer DVD.
The Blu-Rays look pretty good, but I haven’t seen them in true HD because my TV isn’t HDMI-compatible. For years I was resistant to upgrading to BRs, buuuuut I couldn’t resist all that bonus material… 
Okay, now I’ve got some updates!
All the VHS versions are gone, and have already been replaced with Blu-Ray combo packs.
So now it’s like this:
DVD
The Incredibles
Cars
Ratatouille
WALL-E
Up
Toy Story 3
Cars 2
Pixar Short Films Collection, Volume 1
Pixar Short Films Collection, Volume 2
Cars Toons: Mater’s Tall Tales
Blu-ray
Toy Story
A Bug’s Life
Toy Story 2
Monsters, Inc.
Finding Nemo
Brave
You know, I sure can’t wait to get Monsters University!
By the way, I only own one edition for each of those titles. Darn, I wish I had more! I wonder what the bonus features are like…
I’m still debating on whether or not I should upgrade Ratatouille and WALL-E. Ratatouille especially… agghhh not enough features!!! 
WALL-E would probably be OK, since I own the deluxe DVD version. But I am so upgrading Cars… going from used fullscreen DVD to 3D Deluxe Collector’s Edition Blu-Ray! Gosh, I can’t wait! And obviously, MU will be in glorious HD Deluxe Blu-Ray as well… 
I can’t wait to get Monsters University, too, ObsessedWithPixar! It is gonna come out in a week from today! Hey, are you trying to upgrade for the bonus features? I’m trying to do that, too. Here’s why:
I own a Fullscreen 2-disc edition of The Incredibles on DVD. Recently, I found out there was a studio story in the Blu-Ray combo pack version and it’s called Gary’s Birthday. This edition I currently own has Jack-Jack Attack, Boundin’, and Mr. Incredible and Pals. Plus character interviews with Mr. Incredible, Elastigirl, Frozone, and Edna Mode. Plus an alternate opening and deleted scenes such as Snug.
My Cars DVD is full screen and contains the Epilogue, One Man Band, Mater and the Ghostlight, plus 4 deleted scenes such as Top Down Truck Stop and Community Service. Plus a featurette called Inspiration for Cars–with John Lasseter!
My Ratatouille DVD is lacking bonus features.
As for the rest of the films, my sister owns a 10th anniversary edition of the Toy Story DVD, and I own the Blu-Ray combo pack version of the original Toy Story. I wonder if the edition my sister owns contains the so-called Toy Story Treats…
^Yeah, the only reason I want to upgrade them is because of the features. HD is nice, but my TV isn’t HDMI-compatible, so really all I care about right now is the features. It’s the whole reason I stopped buying DVDs to begin with! I mean, the Ratatouille BD has a commentary, for one thing (and I love commentaries like crazy). I think Cars has a whole other deleted scene, and I bet the new 3D edition will be looooooaded with stuff I own all but four films on BD, and Nemo and WALL-E have enough features that I may not upgrade them (although I have heard that FN has awesome 3D, so I’m sorta considering it). But yeah, Cars and Ratouille are definitely getting upgraded.
And yessssss MU is a week away! Of course, I’ll probably just get it for Christmas, so it’ll be a while… ah well, I don’t mind the wait too much; makes it more exciting! 
I think I’m going to give in and buy a Blu-Ray of Monsters University. 
I own all the other Pixar movies on DVD, but I’m going to pay a few dollars more and get some decent bonus features.
I still need to upgrade all of the Pixar films I own to Blu-Ray. I’m sure the next home video format will be out by the time I do so, haha.
All of mine are on DVD and I have yet to upgrade to Blu-Ray. Though I believe I’m getting a Blu-Ray player for Christmas so I can work on upgrading them then. Tho I think my Monsters U will be a Blu Ray version
I’m planning to get Monsters University tomorrow- On bluray. I need those special features!
The DVDs are ripoffs. In July I bought Monsters Inc on DVD. NO BONUS FEATURES. And when I so NO BONUS FEATURES I mean they didn’t even put the fake gag real that usually plays during the credits.
Ridiculous.
At least we’ve got combo packs! You know, a Blu-Ray player can play both Blu-Rays and DVDs. Mine is actually a computer.
UPDATED from 2010
VHS:
Toy Story
A Bug’s Life
Toy Story 2
Monsters, Inc.
Finding Nemo
DVD:
Toy Story
Toy Story 2
Finding Nemo
The Incredibles
Cars
Ratatouille
WALL-E
Toy Story 3 (new)
Digital HD:
Monsters U. (new)
I also have a separate disc that contains tons of bonus stuff from TS/TS2.
^Still have your VHSs, very nice!
That is just wrong 
. Hence why I no longer buy DVDs…
I gave in and bought my first Blu-Ray (MU) last weekend. It feels SO GOOD to finally have some decent bonus features.