Which song do you absolutely HAVE to dance to every time you hear it?
That's easy: Janet Jackson's Together Again. It just makes me smile, maybe not a beautifully as "Janet Jackson's Smile" but it just hits me in the right place. Not the greatest by any means, but hey, this is about what moves us, right?
And when it first came out I could still dance, even dance 20-somethings off the floor. And the club where I was had a huge projection screen, with wonderful lighting effects, and it was sorta like my Last Hurrah out there, dancing to Janet.
So I have special memories of this song, in club remix, and my feet start moving when sometimes a club will still play it, years later, though I can't even attempt it any more. Fond memories, now sad memories...