I made a huge playlist of super positive and energetic songs (called "Positively Positive!" of course). Whenever I don't feel so positive, I put it on random and dance around. It's nice to really listen to the music & dancing can release that stress and negativity. It helps to sing out loud, too.
Some of my favorites are:
"Put Your Records On" - Corinne Bailey Rae
"Say Hey (I Love You)" - Michael Franti & Spearhead
"Love Today" - MIKA
"I Believe in a Thing Called Love" - The Darkness
"You Make My Dreams" - Hall & Oates
I have the full list in my blog for those who want to see more!