Editors' note, July 8, 2015: See CNET's guide to Internet radio services for a more up-to-date evaluation of this service, along with an analysis of how it compares to competitors.
Slacker Radio is a great option for listening to streaming radio with an intuitive interface that makes it easy to find what you want quickly. To use Slacker you must sign up for an account or log in with your Facebook or Google+ credentials.
After logging in, Slacker's interface gives you several options for launching stations. You can search for artists using a field at the top, check out the Music Guide curated by Slacker, or search by genres, stations you've previously listened to, specialty stations, or news, talk, and sports stations. Each selection on the first screen leads to another list where you can swipe to browse selections to find the stations, genres, and music you want to listen to.