I can't really argue against "Still Tippin" because it really set off that whole Houston movement. I think these are contenders though:
^^^ Can't believe this one wasn't mentioned. That song defines that whole period where The Neptunes ruled the radio.
^^^ Had multiple producers flipping Middle Eastern and Indian samples. Just Blaze came with Freeway's "Flipside" and Erick Sermon's "React". There was Nore's "Nothin" produced by The Neptunes and the Truth Hurts song produced by Quik. Yeah, it came out late, late 1999, but it was an official single in 2000.