"I Can See Clearly Now"
"What A Wonderful World"
"It's The Most Wonderful Time Of The Year" (technically, a Christmas song, but you didn't say they couldn't be)

Dear Morrigoon (and Cherny),

"I can see clearly now" and "What a Wonderful World" are my #4 and 5 respectively.

In fact, I created a video presentation of the first 16 years of my eldest daughter's life for her birthday party - and used #5 as the soundtrack. It was awesome, and her dozen or so friends gave me huge compliments (while I was quietly all choked up).

Love and hugs,

The Stoat XXX.

Well coming from an older generation and different genre of taste:

For Good - wicked sound track
Life is a Highway - Rascal Flatts
Hawaiian Roller Coaster Ride - soundtrack from Lilo & stitch

Lots of songs make me happy. The list is huge and changes all the time. But in answer to the OP's question, I'll go one step further.
I'll tell you and show you.

Sunchyme ~ Dario G

Slow (Chemical Brothers Remix) ~ Kylie Minogue *

Love Will Never Do (Without You) ~ Janet Jackson

These three always, always cheers my sad ass up when I'm gloomy.

A runner up is:

Tears Dry On Their Own

Even though the words say it's a sad song, the music lifts my spirits.

The following are ones I love, too. :)
*This one was not chosen to butter up the Australian OP's.
:D

Manhattan Transfer's Java Jive

Benny Goodman's Sing, Sing, Sing

Nat "King" Cole's Route 66

I keep thinking the thread title is the name of the new Disney cruise ship.

I just heard this playing in the background of a Sopranos episode and I had to add an alternate 3:

Dave Brubeck's Take Five

and

Vince Guaraldi's Linus and Lucy (should have been in my original three, but it fell out of my head, Route 66 took its place)
Henry Mancini's Baby Elephant Walk

There are a boatload more, but any of these pieces of music can instantly improve my mood.

The theme song to Bonanza

Pride and Joy - Stevie Ray Vaughn

The Bird - Morris Day and the Time

Nellie the Elephant - The Toy Dolls

Those songs all get me giggly (or at the very least, smiling).

Halcali's Strawberry Chips may now be in the running.

What do they taste like ? :p

Oh, and I forgot to mention:

A Swinging Safari - Bert Kaempfert. :cheers: