Twist and Shout (Beatles version)
I don’t know how you can listen to that without singing along, tapping your foot, and smiling.
ETA: Hey Bumbershoot, that was my second choice!
And I seriously considered naming “I Want to Hold Your Hand”!
Great minds etc…
From the Carpenters I prefer Sing a Song.
If one does not feel good when the kids begin to sing you are not human. 
What I like about you, Romantics.
I don’t know about you guys, but whenever I hear The Pointer Sisters - I’m So Excited, I gotta get up and strut my stuff.
cue hairbrush singing
I didn’t like that song when it was a hit, but now, I can really hear the joy in his voice.
For me, the ultimate feel-good ALBUM is R.E.M.'s “Murmur”. You simply cannot hear this masterpiece and stay in a bad mood. 
Whenever I hear this song, or hear or read about it, I think about the elementary school talent contest at my school when a boy who couldn’t carry a tune in a bucket and who I now believe was probably autistic sang it, and got a standing ovation - and not a mocking one, either.
“Walking on Sunshine” was my first thought, too, though some of the other songs mentioned in the thread are definite contenders.
My last girlfriend and I lived only a few minutes’ walk apart in southwest Moscow. We rode the Metro home when we were through teaching our respective classes in the evening, huddled together and singing the Beatles’ Eight Days a Week. I was disappointed when she declined to marry me, but I will always think of that as “our song.”
That’s another great choice, and although I don’t want to harp on about The Beatles, a lot of their early stuff was very happy and bouncy. I’m Happy Just To Dance With You is another great example.
“I’ve Been Searching So Long” by Chicago. Always loved that song.
Songs that make me do the car boogie:
My Sharona, The Knack
Long Cool Woman in a Black Dress, The Hollies
I agree with (at least some of) the songs already posted, and add
Bright Side of the Road - Van Morrison
Wings of a Dove - Madness
Don’t Worry Be Happy. Bobby McFerrin
More than a feeling. Boston
Good Vibrations. Beach Boys
It has to be…
***QUEEN
Don’t Stop Me Now***
