If Twitter is good for one thing, it is for promoting whatever it is you have to sell. Some of the best self-promoters out there are rappers, and they've taken to Twitter just like every other type of celebrity. Just as Twitter can drive traffic to Websites , it can also drive music sales on iTunes. On a panel at the 140 Characters Conference yesterday, Xavier Jernigan ( @xjernigan , the director of digital marketing at Universal Motown Republic, described how Twitter help put one of his new artists, Asher Roth ( @asherroth ), on the map. Roth released his first album, Asleep In the Bread Aisle , on iTunes on April 20, a Monday. The night before he Tweeted out to his followers (he currently has 69,566) that the album would be on iTunes. And then he Tweeted out a short link which opened up to the album page in iTunes. With no other marketing, the album rose to become the No. 1 digital album for the week. Since then, it has sold about 100,000 copies.