My top 5 for Pixar films always seem to change, but I'm gonna stick with this list for now:

1. The Incredibles- not only awesome (the action's amazing!), extremely well-cast (Holly Hunter as Elastigirl! Jason "Brodie Bruce" Lee as the main villain! Samuel Mother-f'ing Jackson as Frozone!) and exciting, it also has some of the most biting, hilarious satire to come from any film in the past 10 years.
2. Toy Story- It's "Toy Story"- 'Nuff Said.
3. Wall-E- Everyone knows why this movie is amazing, so I'll move on.
4. Ratatouille- Honestly this is the Pixar movie I thought I would completely hate, and It's the most underrated one IMO. The animation is absolutely gorgeous and the characters are lovable, warm and friendly. Out of all the Pixar films, this is the one I'd most like to see a sequel to.
5. Finding Nemo- "Up" might take this film's place when I watch it again (either in theaters or on the inevitably gorgeous Blu-Ray), but overall "Nemo" is heartfelt, well-paced, sweet...and also hilarious.

"Up" comes in right around number 6. It's possibly the most emotional film they've done, but it's a bit all over the place for me. The "buddy comedy" of the film is amusing if unspectacular, but it's the relationship between Carl and Russell, and especially the beautiful, emotional flashback scenes with Carl and Ellie that make this film resonate with me. If the film only had scenes w/ Carl and Ellie, this might have been the best animated film ever. As it stands, it's only one of the best.

1. Wall-e
2. Finding Nemo
3. Toy Story
4. Toy Story 2
5. Ratatouille

Not having seen up
The Incredibles
Wall-E
Rataouille
Monsters Inc
Toy Story 2

1. Finding Nemo
2. Toy Story
3. Ratauille
4. Toy Story 2
5. Incredibles

Haven't seen up yet. And I must be one of the few that really didn't like Wall-E. I thought the animation was amazing... and that is all the good I can say.

I haven't seen Up yet. I think my top five would be the same as yours and I'd throw in Finding Nemo in place of Up for now. Toy Story is easily number one.

I still haven't seen Up, but here's how the other ones rank:
1. WALL-E (Best movie of 2008, best computer-animated movie I've seen)
2. Finding Nemo
3. Monster's Inc.
4. Toy Story 2
5. Toy Story
6. A Bug's Life
7. Ratatouille
8. The Incredibles
9. Cars

Haven't caught UP yet... looks great though

1 incredibles
2 wall-e
3 toy story
4 ratatouille
5 toy story 2

Ugh I cant choose

Toy Story
UP
WAlle-E
Finding Nemo
Ratatouille
A Bugs Life
The Incredibles
Monsters Inc.

Nemo HAS to be in the top 5...not only is it their biggest money earner, it is a great film all together. UP was good, but i would watch Nemo for the 100th time before I would watch UP for the second time...

Hmm that is a hard one. I really liked UP and it will take some time to rank it but...

1. Toy Story
2. UP!
3. Monsters Inc
4. Finding Nemo
5. Bugs Life

I did not like Wall E or Ratatouille at all : (

1-Toy Story
2-Wall-E
3-Toy Story 2
4-Up
5-Ratatouille

I have not seen Up yet either, but I'm pretty excited to

1 - Toy Story
2 - Monsters Inc.
3 - Incredibles (hated it the first time, no idea why, but it's so good now)
4 - Finding Nemo
5 - Wall E
6 - Ratatouille
7 - A Bug's Life
8 - Toy Story 2
9 - Cars (Absolute junk)

That was incredibly hard, I had a really hard time not putting most of them in the top 4 somewhere.

WALL-E
Finding Nemo
Toy Story 2
Monsters Inc.
Cars

(Ratatouille is extremely close with Cars in my Top 5.)

Up doesn't get released in Australia until September!!!! =(

Haven't seen Up yet either but pending list is as follows...

1. The Incredibles
2. Ratatouille
3. Toy Story
4. Wall - E
5. Cars
6. Toy Story 2
7. Monsters Inc.
8. Finding Nemo
9. A Bug's Life

I'm not sure... the only Pixar films I can remember being released are WALL-E and Ratatouille, and they both had September releases. I know WALL-E was several months earlier in the US, but I'm not sure about Ratatouille.

It's still annoys me, though.

1. The Incredibles (Complete, on all levels for me)
2. A Bug's Life ( Put Dreamwork's Antz to shame. Great characters.)
3. Wall E ( so little dialogue in the first act, makes this a rarity in American Cinema- brilliant production design)
4. Monster's Inc ( Imaganitive design and story)
5. Toy Story (Classic picture as an early feature length digital 3D- a bit too talky for me).
6. Finding Nemo (Beautiful design, but way too much dialogue)
7.Toy Story 2 (can't rank sequals too highly, but as funny as the first)
8.Ratatouille ( Great visually, but underdone story)
9.Cars- (Good for fans of NASCAR, but no-one else- weakest story. Looked like a feature length ad for toys- a pity given it's technical brilliance).
Up hasn't been released in Australia yet.

Just saw "Up". Forgive me, but I was a little disappointed... all the buzz (every pun intended) was that it was the best film from Pixar ever. I politely disagree. While still a fantastic movie by every other standard, I found it the be somewhat heavy-handed and strangely sad for a Pixar film. And the funny parts don't hold a candle to the hilarity of some of Pixar's other efforts. That said:

1. Finding Nemo
2. Wall-E
3. Ratatouille
4. Toy Story
5. Toy Story 2
6. The Incredibles
7. Monsters Inc.
8. Up
9. A Bug's Life
10. Cars

PS - I think 1-8 are totally open for debate. 9-10 are a given, though... while still really, REALLY good films, they rank at the bottom of nearly every list of this type.

What I really like about Pixar is their well-spun stories. Gorgeous visuals don't work for me without the foundation of a real story. This is my Top 5 Pixar Features.
1. Wall-e (for bringing character silence back on screen, wow!)
2. Finding Nemo
3. Toy Story
4. Up
5. Monsters Inc.