Ralph, go here.
Google is your friend.
Rico beat me to it, but my “incoming mail” noise is a foghorn. It’s not the Addam’s Family foghorn (so it doesn’t have the canned laughter in the background) but it’s pretty similar. I’ve had that for a couple of years, and I love it.
Dennis Miller.
Several hard drives ago, my incoming mail sound was “[twannnnngggggg] Message for you, sir,” while my error message was, “I…I don’t know that—WAUUGHHHHH!”
Windows start: The “going to commercial” music from MST3K
Windows close: Crow saying, “Bite me, it’s fun”
New mail: Letterman saying, “Congratulations, Skippy, you’ve got mail”
ALL SIMPSONS
Startup: Professor Frink “Oh dear, I’ve redorkulated!”
Program Error: Homer “What the hell was that?”
Critical Stop: Homer “Sweet, merciful crap!”
Shutdown: Ralph "Oh boy slpee
DAMMIT :smack:
Shutdown SHOULD be Ralph: “Oh boy sleep! That’s where I’m a viking.”
stupid enter key. . .
I have “What is Thy bidding, my Master?”
And Mick Jagger “You’ve got some letters.”
Wanna trade?
All of this is very cute, and funny – the first two or three times you start up your machine. After trying out a number of different sound files, I’ve just gone back to the defaults.
It’s embarassing when Darth Vader starts the laptop, but I hate the default star and exit Windows WAVs.
Psycho theme on boot up.
Womans scream on shut down.
Scared the heck out of one of my students when I changed to these on my office comp.
I do have a two-minute .WAV file of the campfire scene from “Blazing Saddles”… I sometimes put that on the startup of my coworkers when they aren’t looking…
I have threatened to set my 13yo daughter’s start up sound to a recording of me saying “Do your homework FIRST.”
The funniest thing EVER was when my (former, though this incident had nothing to do with me leaving) boss was leaning over my shoulder as I was correcting some document on my computer. He asked me to open another document for comparision, but I got an error message. Complete with Wesley from B:tVS intoning:
“Bitch. (pause) Not you, obviously.”
He looked at me, horrified, and said “Did your computer just call me a bitch??” I couldn’t answer, as I was laughing too hard. For days. 
Now I have a fair mix of LOTR and South Park sounds, though I’ll probably be changing them soon.
Link, please?
Signed, Wesley’s bitch.
Drop me an email reminder and I’ll see if I can pull up that link for you (addy’s in profile).
The only one I’ve ever bothered changing is the Windows start up sound. Currently, I have Zoe from Firefly (“Out of Gas”) saying “You paid money for this, sir? On purpose?” (I built the computer myself, and have a love/hate relationship with it when it crashes.) I used to have the Emperor Palpatine from Return of the Jedi saying “Now witness the firepower of this fully armed and operational battle station!”, 'cause I often run the computer with the cover off, so it looks like it’s only halfway completed.
Windows start up: “Welcome, pilot! How ya doin’?” from Invader Zim. That’s about the only one I’ve changed.
Received, installed, and now my shutdown aria-thanks
Start Up : the complete *Der Ring des Nibelungen *, pretty slow though.
I’ve got them both.
Most of what I use, I get from either http://www.wavcentral.com/ or http://thefreesite.com/Free_Sounds/Free_WAVs/ .
Enjoy!