I heard a song at Starbucks a couple of years ago that's bugging me. It's from the mid 1960s or so. Two female singers in harmony. I think it may have been in triple time.

The hook in the chorus is the most memorable: "Ay, ay, ay!" sung in three long notes, outlining a minor chord going upward. (A, C, E if you're in A minor.)

Any ideas?

Reminds me of an old Mexican song called "Cielito Lindo".
If so, you are probably looking for a version by someone like The Lennon Sisters.

Most wild guess ever........It's the first thing that came to mind.

Dee Dee Sharp - "Ride"

http://www.youtube.com/watch?v=HBNPhF1N6CA