For me... "Sugar Pie, Honey Bunch (Can't Help Myself)" is definitely one of those. And any song similar. I love motown. Hahaha.
It works every time This song is second on my list https://www.youtube.com/watch?v=W5FfJ89rGPc Hotwater
This one usually brings me up when Im down https://www.youtube.com/watch?v=-rjMB0JotHM&feature=related
Smoky Robinson's Tears of a Clown does it for me too, though it's really not meant to be a happy song, his voice is so cheerful.
this one makes me happy too, cuz I'm usually high or getting high when i hear it https://www.youtube.com/watch?v=8cNFGjtGlrU
https://www.youtube.com/watch?v=kkVjd1fJMME this is my number one happy song. :] been listening to it lots lately.
The parade's still passing by old folkie carefree highway sunshine superman sunshine go away today six string orchestra there are others./