I've recently accepted the fact that Ive got a little chemical in my brain that is trying to wreak havoc in my life. I found that one you accept it, it's easier to find a way to work through it.
If I put a station on my Pandora like Walking on Sunshine Radio and 'Jump in the line' by Harry Belafonte pops on I find it irresistible to smile. Slightly classic music that makes me wanna dance and crow along always improves my mood. When ever I'm feeling the blue coming on i throw in a ear bud and let it take me away for a little while.
Here's a few songs that bring on that smile for me, maybe they'll work for you
'Jump in the line' by Harry Belafonte
'The Lion Sleeps Tonight' by The Nylons
'Sweet Pea' by Amos Lee
'R-E-S-P-E-C-T' by Aretha Franklin