Mine is "Toy Soldiers" by Martika:
It's a total chick song, and a pretty melodramatic one to boot. Plus she got her start on Kids Incorporated, a TV show where mostly pre-teens sang hit songs and acted cheesy skits in between.
But that melody is just so damn catchy, and since it isn't repetitive, it should be harder to remember than the average pop song. Still I always find myself singing it the rest of the day whenever I hear it. And it's got the right amount of variety, novelty, and distinctness in the sound textures -- unlike the faggy indie, techno, etc., songs that become so self-absorbed in their exploration of texture that they neglect basic things like melody and harmony. Just an overall really well crafted pop song.