I already did "I'm Yours", which is a song I danced to with my best friend/husband. Let us go back in time to my waltz party days at St. John's. I had several favorite dance partners, so it is hard to pick a song that went with any specific one person. I guess I'll go with "Hell" by the Squirrel Nut Zippers. I know, the name suggests it wouldn't be a very cheery song, but it is very uptempo and has awesome trumpet solos. My roommate and one best friend Kat liked it; she didn't come to waltz parties often, but when she did, she would dance this one with me. Jonathan, another best friend, also danced this song with me. It's a good song for dancing vigorously!
I almost forgot another very special moment and song from St. John's. In the fall of my senior year--when I was one of the co-archons (co-presidents) of the Waltz Society--we held a '50s themed dance. It was really fun; we got some friends to make milkshakes and wear little "soda jerk" hats that I begged off of the local Red Robin restaurant. We played lots of '50s and '60s tunes in addition to our usual swing standbys. Towards the end of the night, we played "Oh what a night" by Frankie Valli, and for some reason, it just felt like this super special moment: several friends were gathered in a circle, dancing, grinning, just loving life at that moment. I have such fond memories of that party.
Finally, a song you could listen to all day long: oh my...all day? Then it might have to be something that's kind of on the long side and classical. I'll go with J.S. Bach's "St. Matthew Passion" (another thing that I discovered at St. John's, that wonderful college!), and in particular, "Erbarme Dich"