“Just what makes that little old ant
think he can move a rubber tree plant…”
Bobby McFerrin
(too lazy to code at the moment)
Tie:
“Jessica”, by the Allman Brothers
“Rosalita”, by Bruce Springsteen
Got in a car accident once, these were the first two songs I heard driving away, and by the time they were over I didn’t care about the pending lawsuits.
Higher and Higher, by Jackie Wilson.
I just love that one, even if it is sickeningly sweet.
Yummy!
And let’s not forget the Abba catalogue.
Some folks missed the word “sickening”. I nominate "I’m the Happiest Girl in the Whole USA by Donna Fargo. I’m feeling a little nauseaus typing this.
Zip-a-dee-doo-dah,
Zip-a-dee-yay
My, oh, my, it’s a wonderful day
Plenty of sunshine
Headed my way
Zip-a-dee-doo-dah,
Zip-a-dee-yay
Mr. Bluebird’s on my shoulder
It’s the truth…
OK, this isn’t sickenly sweet! But it does make me happy.
I can’t believe nobody’s mentioned “Mmmbop” by Hanson yet. I ended up with a free copy of their CD, and I must say, that’s a good corny/happy song to sing along with while driving on the highway.
-Andrew L
Tee-hee, I have that on my computer when Windows loads. 
I consider “Keep on the Sunny Side” from the Oh Brother WAT soundtrack my personal pep-theme song. Can’t help but sing along and smile.
Too obvious.
Another nomination for today: Moby “In My Heart”, from his new album 18. Beautiful stuff!
Pop Goes The World by Men Without Hats
Hearts Are Trump by Trio
Petula Clark - “My Love”
That is exactly the song I was going to mention. I have an MP3 of it on my computer, and as soon as I saw the thread title, I played it. 
“Wouldn’t it be nice” by the Beach Boys.
You are my sunshine,
My only sunshine.
I’m looking over a four-leaf clover
That I overlooked before.
It’s like a jungle
Sometimes it makes me wonder
How I keep from going under.
…
Sorry … not so cheerful, but for me it has sentimental value.
It’s a Bugs Bunny song, I think he sang it in a short featuring Yosimite Sam.
“Lookin’ through the knothole in grandpa’s wooden leg, oh who will wind the clock when I am gone? Go fetch the axe there’s a flea in grandma’s ear” etc.
Bike, by Pink Floyd.
I know a mouse and he hasn’t got a house
I don’t know why I call him Gerald
Hehe…
You’ve got to include Roger Ruskin Spear’s version of “Make Yourself A Happiness Pie.”
You can listen to it here and it starts at 1:24:35 in the program.
Then there’s always :
Singing In The Bathtub
Magidson/Washington/Cleary
You can hear a 30 sample here for the tune.
Singing in the bathtub
Sitting all alone
Tearing out a tonsil
Just like a baritone
Singing through the soap suds
Life is full of hope
I can sing with feeling
While feeling the soap
Oh the ring around the bathtub
Isn’t so nice to see
But the ring around the bathtub
Is a rainbow to me
I can yodel opera
Even while i scrub
Everybody’s happy
While singing in the tub
Never take a shower
It’s an awful pain
Singing in the shower’s
Like singing in the rain
Oh there is dirt to be abolished
But don’t forget one thing
While the body’s washed and polished
Sing brother sing
Be my love, for no one else can
End this yearning
Reaching for a towel
Happy once again
Watching all my troubles
Go swirling down the drain