If there was one song that I believe had sealed Madonna's then already indelible place in pop music, that would be Vogue. Released in 1990 as the carrier single of her I'm Breathless album, Vogue was one of those dynamite chart-toppers destined to be a classic. According to Wikipedia, Vogue is Madonna's most successful single of her career prior to the advent of digital distribution.
When the song was featured in the film The Devil Wears Prada, it still sounded very "now" despite the fact that it came out 18 years ago. Here's one of the Madonna's first public performances of the song, from the 1990 MTV Video Music Awards. I find the performance simply brilliant, even though Madonna lipsynchs the entire time.
Just recently, Rihanna performed the song during the Fashion Rocks special. I love the arrangement--very Rihanna--but the last quarter of the song needed more oomph. The performance could have been a little more hard-edged, but maybe I'm biased because of the whole Bellestars/Alma Moreno motif going.
Anyway, I hope she releases it as a single.