This was not a good year for mobile music. Ringtones sales are declining, over-the-air downloads are still little more than a blip on the radar, and the potential of ambitious initiatives like Nokia's Comes With Music is still unknown. There's one shining exception: Apple's iPhone.

The second-generation iPhone unveiled this year features faster wireless download speeds comparable to broadband, thanks to AT&T's "3G" network.

Speed and slickness aside, the phone's potential may lie in Apple's App Store-a groundbreaking new system that lets software developers create and sell programs. Given the iPhone's heritage, it's only natural that some of the most interesting apps involve music. Here are the ones that changed the game.

1. Pandora (Free)

This online radio service has always been a favorite among geeks, although some question whether the company can convert that interest to real profit given the increased licensing fees for streaming music. One key could be Pandora's iPhone app, which lets users access their existing Pandora stations. Since it launched in June the app has been downloaded more than 2 million times, doubled Pandora's number of new users per day to 40,000 and generated up to 10% of the service's streaming activity. In doing so, it has opened the door to other mobile streaming music apps from Clear Channel, Last.fm and imeem.

2. Tap Tap Revenge (Free)

For the full article, including apps that let users create their own music, song indentification apps and more, click here.