Apple Computer's ( AAPL) iTunes may dominate the legitimate market for digital music, but that doesn't mean the company's competitors are sitting still. On Tuesday, Time Warner's ( TWX) AOL division relaunched its Music Now download service, adding streaming Internet radio and thousands of music videos. Separately, start-up company SpiralFrog announced a new advertising-supported music download service that will feature music from Vivendi Universal's Universal Music Group. Both companies made an effort to differentiate their services from the competition. Music Now users who sign up for the site's subscription service will be able to download and play as many of the music videos available on the site as they'd like, something they couldn't do elsewhere, AOL said. iTunes, for instance, offers music videos only on a pay-per-download basis. Likewise, SpiralFrog is attempting to create a new type of download service. Instead of the iTunes a la carte model or the subscription services offered by other download sites, SpiralFrog plans to rely on advertising for its revenue. In other words, SpiralFrog users will be able to download songs for free, in exchange for watching or listening to advertisements on the SpiralFrog Web site. Interestingly, SpiralFrog's service seems to be pitched to users of illegal file-swapping sites as much or more than it is to iTunes users. In a statement, the company emphasized that its service will be free and legal and devoid of the spyware and viruses that have infested file-swapping sites.