The familiar wooden ‘plop’ of a popup blocked by google toolbar.
The laughter of toddlers.
“Meow”
The knock at the door which implies an anticipated parcel delivery.
The cracking of ice-cubes when liquid is poured over them.
The sound of rain when you are indoors.
Ditto the laughter of children.
That sound effect from Lost in Space when something suddenly disappeared.
A laser printer “winding up” to print.
The Enterprise’s phasers from the old Trek.
The sound the disc drawer on my Panasonic DVD recorder makes when it closes.
a falcon (or whatever that bird of prey is that makes a high pitched caw). link anyone?
borla exhaust system
hydraulics
pneumatic tools
The sound of pills rattling in an HDPE bottle. Weird, I know. Lucky me, I work in a pharmaceutical lab, so I get to hear it all the time, without even having to go out of my way for it 
The wind whistling through pine trees.
-The creepy sound effect used in the movie Assassins, right after…
…Stallone says “I told you to wait” to Julianne Moore when she runs back to her apartment.
They used that one on the “Dennis the Menace” cartoon, a lot. 
Anyway…
-The sound of my CRT monitor powering up.
-Robocop’s footsteps.
-Zeppelin engines.
That reminds me of a smell I like. Namely that of a several-week-old pine tree in the middle of town.
A child laughing
A cat purring
A Dobro
A woman climaxing
Purring cats.
The way my husband says, “Whatchu doin’?”
The way my sister deliberately mispronounces my name.
Rachmaninov.
The rolling ball noise on Zuma.
The noises by an old pinball machine that used to be in the Columbus airport:
“Lionman! Lionman! Bwahaha!”
“Go through the tunnel.”
The “hiya!” frog from the isp commercial.
All of the sound effects from the old Mac game “Crystal Quest.” Boing! Boing! B-boing! Blebbem. Blebbem.
And the sound of Mario shooting fireballs.
If we’re talking arboreal smells, then I nominate wet plane tree leaves.
The silence of the Rockies in the morning. Had tinnitus for over 25 years now. I’ll never hear it again. Would give almost anything.
A train going through at night.
The crack of a soda can opening.
The riffling of pages on an old book, where the edges are worn soft.
My toddler’s latest sentence.
“In the not too distant future…”
There was a pinball game I played in the 70s: Williams’ World Cup. When you got the full bonus with the 5x multiplier, it made a cool “warp” sound after the ball was played out. I also liked the sound the ball made when the kicker slammed it against the underside of the glass.
FSSSHHH!! – the sound of freshly poured Coke fizzing over ice
FWOOF – the sound of the furnace kicking in on a blustery winter day. Nothing says security like that sound.
YOWP! – The funny noise our dogs make sometimes when they yawn.
HNGGGG, HNGGGG – The sound one dog in particular makes in the morning when she’s snuggled in the bed between us. It’s a sound of utter contentment.
“Happy Modem Noise” – I have no idea how to spell it, but you know what I mean: the handshaking noise that means your modem is working. I keep it turned on so I can hear it. A new-computer-user friend of mine was over once when I was dialing up and said, “What is that horrible noise?” but I explained why it makes me happy.
The sound of the car pulling in when Mr. S comes home from work, and the accompanying joyous barking of the dogs (in case I missed it).
FWOOOOOOOoOooOoooOooooooooooOOoOOoOOOoooooommmmm
The sound of a data center with a couple hundred racks of servers powering down after someone turned off the (really big) UPS in an attempt to silence the alarm, which was obnoxiously beeping due to an in-progress generator test.
It happened where I worked, and I would have LOVED to have been there to hear it. I can only imagine. If I ever retire, and they forget to revoke my access after I’ve left… 
The first 8 opening beats of any Final Fantasy battle theme up until FF 7.
The sound of fingers drumming on a hard surface.
Clicks, especially the wierd clicks in some African langauges.
Unusual technoish guitar riffs.
Church chiors.
Feedback.
The sound effect used for the Hypnotoad from Futurama. All glory to the Hypnotoad.
A cat purring.
Birds singing just before dawn.
Crunchy footsteps in the snow.
Rachmaninoff.
“I love you.”
Moaning lovemaking.
A cello.
A tenor singing.
A horse clopping on a city street.
The sound my cats make when they jump up into bed.
The whispering silence of the snow falling
Waves rolling up onto shore
My babies breathing when they are deep asleep
The phone ringing noise when I get an email from my boyfriend
Pachabels Canon
my doggies contented snores
the coffeepot gurgling
horse shoes on cement
The wind in aspen leaves
rain
Running water.
The moment of silence followed by the communal “Aaaaaah…” when you have five people taking whiskey shots all together. Beautiful.