There are a lot of songs I like, but I haven't put much thought into what songs actually make me happy and smile.
That being said, here are the few I can think of off the top of my head (I am certain there are more):
Renegade - Styx
Eat the Rich - Aerosmith
I'm Yours - Jason Mraz
Simple Song - The Shins
With Arms Outstretched - Rilo Kiley
Unwritten - Natasha Bedingfield