To balance this thread:
ALL Windows event sounds. They sucked when I used 3.1 and they suck on XP (which is why I always turn them off or replace them).
The squeal of disc brakes.
That cracking sound my wisdom tooth made when the dentist pulled it out.
Someone throwing up.
Megan Mullally’s voice on Will and Grace.
[morty]That tearrrring sound.[/morty]
The sound of someone yawning and then sighing at the end sends me up the wall. Also, any smacking sound in kissing is enough to send me over the edge. Short, soft, smacking kisses are the worst.
Breaking glass. Every time glass is broken near me, I get an adrenaline rush like you wouldn’t believe.
Puking. It’s not the sound so much as the sympathy hurl it invokes.
The guy in the next cube eating potato chips. He eats so noisily I want to beat him with a crowbar.
High-pitched noises, like someone rubbing a balloon (squeak squeak) or a balloon being filled with helium (whoosh, occasionally followed by a BANG). This is why I stopped going to the county fair.
Someone smacking their lips when they eat…makes me just want to smack them.
The sound of Dubya’s voice.
And the sound of sports announcers on the evening news who sound like they just inhaled 16 balloons worth of helium and they screech every score as if the game were happening at this exact second.
My clock radio. 'Nuff said. 
Any alarm clock in commercials or my bedroom.
Styrofoam coming out of a cardboard box.
Ditto on the throwing up thing.
This may be stating the obvious but…Ashlee Simpson’s “singing” would rank right up there.
In fact, you can add her sister Jessica to that list as well.
One sound that nearly got me murdered by my siblings was when I was scraping my fork rather hard along my plate to get the last bits of sauce.
Harley-Davidson motorcycles
Beginning oboe players
SQWAWKKKK!AAGH!!!COUGH…cough…death
Styrofoam rubbing against other stryofoam.
The squealing sound my heater makes after about 15 minutes.
Smooth Jazz.
The sound my fax machine at works makes when it is out of paper.
The sound of someone rubbing a balloon.
My kids whining or arguing.
Babies crying.
The sound of something metal in the garbage disposal.
The sound of our alarm system at work that goes off when someone leaves a door open for too long.
Hey, I wondered idly into this thread thinking it was that thread.
I am glad you posted it though because I had some ideas already for hated sounds…
Those extra few clicks when you click on an internet link! (the ones that tell you the site is up to no good)
The sound of another man peeing.
The GOD AWFUL custom alarm sound we get at work when something really minor happens “WARNING, A CONCENTRATOR IS DOWN!” accompanied by a star-trek red-alert sound effect.
fingernails+blackboard.
Badly maintained disc-brakes.
The unnaturally loud TSHH sound trucks sometimes make when they pull up close to you.
My old shoes. (‘squeak’ ‘clump’ ‘squeak’ ‘clump’ ‘squeak’ ‘clump’ ‘squeak’ ‘clump’)
Strong Manchester accents.
Little dogs barking
…and big dogs barking.
The VZZZ sound at the end of an adaware scan, scares the shit out of me every time!
Screaming kids.
Fran Drescher or Ah-nuld speaking
A whip cracking.
Gunfire.
Explosions.
The opening jingle of most McDonald’s commercials lately: “Bah da bup-bup-BAAAAAAAH!” I’m hatin’ it.
Ditto on Dubya’s voice.
The loud crunching sound people make when chewing on nuts, and other hard snack food items. I can’t stand being in the same room with someone that makes such grating and obnoxious noise.
Loud clocks. You can only really notice this in a really quiet room though. Still, annoying all the same when that cursed sound rears it’s ugly hands.
Jimmy Stewarts voice. He always sounds like he’s whining.
Whiney, complaining, music.
Any song where the “artist” tries to sound like a creepy psychopath. Oh, bite me; you’re not scaring anyone. The overall attitude in these songs doesn’t sound like anything I’d expect from an actual killer.
The loud sipping of coffee or the slurping of soup.