Apple's iTunes online store was the third-largest overall music retailer in the United States, leapfrogging ahead of Amazon.com and Target in units sold, a market research firm said Friday. iTunes had a 9.8 percent market share in the first quarter, ranking behind Wal-Mart Stores' 15.8 percent and Best Buy's 13.8 percent, according to The NPD Group.

Survey: iTunes Grabs No. 3 Ranking in Music Sales