We weren't disappointed by Slacker Radio's free iPhone app. After logging on, the dark-themed app lets you simply tap the icons at the top of the stations list to launch favorite and custom stations. Scrolling down, you'll encounter a search option and top music stations, followed by a long list of musical genres; a logical flow for the iPhone's design.
Slacker also takes advantage of the iPhone's height to much more prominently display album art than on other mobile devices. The controls to pause, skip, save, and ban an artist are finger-friendly. You'll be able to edit a station while it plays, but sadly, you must create new custom stations online, not on the iPhone. Slacker Radio also won't flip into landscape mode, and it won't let you send your awesome station creations to a friend.
However, sound quality, speed, and access to tunes are the most important ingredients in a mobile streaming radio app, and this app has them in spades--so long as you stay within Wi-Fi range. 3G speeds were fair, but there were more stops and starts while waiting for songs to buffer.