I did some research - well actually I googled Ralph Eggleston - and you may be right. The dentist looks quite like him in this picture :
Thank you for that, Archibald - you are a champion! I tried googling the image several times but nothing came up. Mystery solved! 
Updated
Sorry it took so long… I kind of procrastinated with updating since it takes about 3 - 4 hours every time, but I’ll try to update more frequently. I’ve updated just about every film’s in-jokes. If you spot any mistakes, please post in this thread and let me know. Next up, I’ll tackle the “bloopers” at the end of Pixar films. I’ve found screencaps of most of the ‘confirmation needed’ in-jokes, but the ones that still haven’t been confirmed have been taken off the list until they are:
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A113: Behind Sulley on the wall just before he thinks Boo got crushed in the garbage compressor. (Monsters, Inc.)
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Some of the scarers’ names on the board are the surnames of Pixar employees. (Monsters, Inc.)
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When Skinner is looking through his letters, one of them has a Roz stamp. (Ratatouille)
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Steve Jobs is sitting near the customers who are asking “What is new?”, and Lou Romano is sitting to the left of the screen when the camera pans out from Remy’s new restaurant. (Ratatouille)
Please remember to read the list before submitting in-jokes, a few of the references you guys are posting are already on the list. Other than that, keep on submitting. We are that much closer to having a really extensive list, and to opening up the short films section. Thanks, Pixar Planeteers! 
Could you guys please help me with a couple of possible references?
Here’s a screencap of a courtroom sketch for The Incredibles, but I can’t figure out which Pixarian’s signature it is in the bottom right-hand corner of the sketch… (Actually, I do have an idea, but wanted a second opinion.)
Here’s a map from a street directory in A Bug’s Life, can anyone recognise the location?
— Rachel. =)
Rachel- The Roz stamp reference and the employees last names in MI are true, the two others are questionable.
The scarer’s last names in-joke was confirmed either in the commentary or the special features of the DVD and the stamp I’m pretty sure features Roz.
The Steve Jobs one is just speculation, I doubt it since Brad Bird calls those characters the food snobs. A113 is supposed to be in MI but its supposed location only says “B” or “13”.
Hope that helped, keep up the great list!
Wow, this thread is amazing! There are sooooo many things that i’ve never realized! lol
Next time I watch the movies, I’ll pay close attention! lol
Martin - Now that you have Ratatouille on Blu-Ray, would you mind getting the highest resolution of the Roz stamp frames and PM them to me, please? Size is not an issue, try to get the image(s) as big as you can. Maybe if we have a clearer picture we can have a better try at working out what it is.
As for the Pixarian names on the scarers’ board, I know that they said this on the commentary, I’m pretty sure I even have a Monsters, Inc. guide book with the names on there, however, I haven’t been able to find their names on the board within the movie. If you have a screencap of that, by all means, please post it here.
I’m actually open to the idea of Lou Romano and Steve Jobs being restaurant patrons in Ratatouille - the Pixarians can take a joke. I may have actually seen them myself, but in the mean time it will be off the list till I do find them, or someone else confirms it too.
I think I read on the Internet that the A113 is in Monsters, Inc. in that particular place, but have never seen a screencap of it. Don’t tell me we have another “Pizza Planet Truck in The Incredibles”-like situation on our hands! Heh.
Thanks for the feedback, Martin. =)
Rachel- I’m sorry, I can’t get screencaps because I don’t have Blu-ray on my computer, but what I can do is look closer for more hidden treats.
I can get you a cap of the scare board though.
Regarding A113 and Monsters, Inc., yup, it seems like we have another TI/PPt mystery on our hands, unfortunately. 
Oh, and I was just wondering if you’ve been updating contributors, I don’t think I’m there.
Thank you for taking the time to maintain the (most complete Pixar in-jokes) list!
Martin - Ah, right. I forgot that most people don’t have Blu-Ray drives… If you could get me a cap of the score board, that’d be great! I don’t know how I’ve managed to miss it after looking for it so many times. I’ve added your username to this list now, sorry about that - the next day after updating I suddenly thought to myself, “I’m pretty sure I forgot to add Martin’s name to the in-jokes list…” Heheh.
Well, thank you very much. I think by now we would have the most complete in-jokes list on the Internet, asides from Pixar’s master copy (if one exists.) I wouldn’t have nearly as much of a list without yours and others’ submissions, but it’s a nice feeling to know that my effort doesn’t go unnoticed. And it makes me want to keep going with it, too. =)
I know for a fact that the Pixar archives has a very vague list. Christine Freeman, the archivist, told me she’s starting a project to confirm and collect this information from the people who worked on each shot. I wonder how it’s going…
Anyhow, I bet the directors have a list or notes of some sort with in-jokes from their respective films.
I’ll edit this post with the screencap later in the day.
Martin - Really? That’s so cool. I’m surprised they hadn’t had a list already. They would have to go through the films’ notes and ask each director, too, yeah. Even then unless every in-joke was written down, I don’t know the possibility of retrieving every single one. Christine might even end up using our list to save time - how ironic would that be? Maybe Pixar will release an in-jokes book in a few years’ time… I hope so.
Guys I’ve found A lot of In-joke for Wall-e, you guys will have to wait until the DVD come out , so then I could post the in-jokes.
I’m late! I totally forgot yesterday, but here’s the screencap of the scareboard, obviously it’s a composite.
Names that instantly stand out (in order)::
Joe Ranft (Story, Heimlich (etc, etc.) RIP)
Bud Luckey (Director of Boundin’. Creator of Woody)
Jonas Rivera (Producer of Up)
Bob Peterson (Co-Director of Up, Roz, etc. etc.)
Bob Pauley (Production Designer on Cars)
Jay Ward (Production manager)
The rest I’m not sure of. I think Pete Docter said that the only afke last anmes (besides Sulley and Randall’s is Plesuski, but I don’t remember if that’s the one.)
Note: I’m adding little fact about the people 'cus I’m bored.
Thanks for that, Martin. What scene is that from? I’ve looked several times but could never find the names…
azzstar - I look forward to seeing what you’ve found.
It’s the scene on the Scare Floor, when it’s time to get ready to start going though doors.
Does anyone have a screencap of the Monsters, Inc. simulation robots? I ask this because I was watching the Incredibles last night and I thought I saw a human character look like one of the simulation robots. The human character I am talking about in the Incredibles can be seen after we see Huph bandaged up and Rick and Bob walking down the hospital halway. Two nurses wheel a man across. I believe the man that was wheeled across looks like one of the simulation robots.
Doesn’t look like the same person to me, would have been neat if it was, though.
Is there more than one simulation robot in Monsters, Inc.?
Roll up, roll up! It’s time to break out your Pixar Short Films Collection DVDs because the short film section is now open! There are plenty of Pixar in-jokes to be found so please submit as many as you can. I can’t wait to see what you guys have found. =)
WALL•E, Presto, and BURN•E will be added to their respective sections after the DVD has been released in the US.
Here’s a scene from Lifted. Tin Toy’s under his bed. Sorry I don’t know if it’s really definite though.
and its linguini in the bed…with tin toy!
Here are some short Film in-jokes I know of the top of my head:
Red’s Dream: Pixar ball texture map on floor, Andre clock
Tin Toy: Pixar’s original logo on bag, toy under couch called RenderMan
Geri’s Game: Pixar original logo on chess box
Boundin’: P. Sherman’s hand, Stanley (Cars), Gurgle model
Jack-Jack Attack: Pixar ball
One Man Band: Newly shorn sheep on Tippy’s tunic
Lifted: Tinny, Linguini model used for Ernie, Aliens are old WALL-E designs
Your Friend the Rat: WALL-E, PT Flea
More refs. soon!