This feels like double-dipping, but it took so long to write this Quora answer it must be acceptable to post it on my blog as well.
“Which is the best AR Rahman song that one must hear for sure?”
My answer on Quora (along with other answers, of course) is at http://qr.ae/7Qvh9, and I’ve reposted it here:
Rahman’s music for the 1995 movie Bombay has been one of the most commercially successful albums in his home country India, and the best selling film soundtrack of all time. It has been recognized on various must-listen lists, including the UK Guardian’s Top albums to Hear Before You Die.
But since you asked for a song, not an album, I’ll nominate one of the songs from this album: कहना. ही. क्या. / kehna hi kya.
Kehna hi kya is one of its most memorable and popular songs, and found its own independent success on the radio. It got additional recognition from the UK Guardian, beyond the other tracks on the album, on their Top Songs to Hear
(misspelled as “kehma hi kya”). Anecdotally speaking, it was ubiquitous in India in the 90s, and is still heard frequently today.
Kehna hi kya wins my vote also because it includes a vocal solo by A.R. Rahman himself, so one gets a taste of him both as a composer and a singer.
The movie Bombay is the story of the love between a Hindu man and a Muslim woman. The story leads up to a turbulent period in the early-1990s, escalating to the inter-religious Bombay Riots in which the Babri Masjid (mosque) was destroyed and hundreds of people were killed.
The song carefully uses language (Urdu-esque) and invokes images (like the veil in the excerpt below) that the audience associates with Muslim culture, but without any actual religious content. The images themselves are beautiful and passionate.
Sharm thodi thodi humko aaye to nazarein jhuk jaayen
Sitam thoda thoda humpe shok hawa bhi kar jaaye
Aisi chali, aanchal ude, dil mein ek toofaan uthe
Hum to lut gaye khade hi khade
Translated (my own translation; I’m no language scholar but I disliked others I found):
A little shyness came and caused my eyes/gaze to fall downward
(But) even the wind tortures/teases me,
Blowing in such a way as to throw off my veil,
— and (likewise) a storm blows/rises in my heart,
Just standing there my heart was stolen.
The lyrics were written by Mehboob Kotwal.
You can download the song from Amazon: