I find songs that make me happy are either those that make me dance or those that remind me of someone or something.
BOOGY ONES
Build Me Up Buttercup- The Foundations <- The ULTIMATE happy song
Stronger- Kanye West
Dance, Dance- Fall Out Boy
Fiesta- The Pogues
Come Go With Me- The Del-Vikings
Sweet Soul Music-Arthur Conley
Ok, so there's a few very varied songs.
if you don't want stuff that makes you dance there's
Everything Sucks-Reel Big Fish
Wonderful World-Louis Armstrong
Bad Day- Daniel Powter
Big Yellow Taxi-Counting Crows
I Will Follow You Into The Dark- Death Cab For Cutie (one of my all time faves)
I'm Yours-Jason Mraz (because come on, no matter how many times it's on the radio, you just can't get enough)
You're My Best Friend- Queen
Mambo N 5- Lou Bega(if that doesn't make you happy, nothing will)
Elvis Ain't Dead-Scouting For Girls
and of course Here Comes The Sun- The Beatles, but if you can get Steve and the Cockney Rebels, their's is happier.
Well I hope it helps