A few of the most popular online radio services are Pandora, Slacker, and Spotify. There are a few others such as Songza, Soma.fm, and TuneIn. There is another one in the works tentatively called iRadio from Apple. It is speculated it will be unveiled next week at WWDC (Apple Worldwide Developers Conference June 10-14.) What will make iRadio different from Pandora is its integration with iTunes making it easy for someone to purchase a song they like. Like Pandora, there will be a free ad-driven version and a paid ad-free version.