The definitive source for rankings of popular new songs is Billboard magazine's Hot 100, available online at Billboard.com. Billboard has been charting popular songs since the 1930s. Since the 1960s, it has been fully devoted to tracking popular music in all categories, including pop, rock, country and R&B.
Visit Billboard.com and click the Chart link in the top menu. From there, you can select the Hot 100, which is comprised of the top charting songs from all genres, as well as charts for each specific music category that make up the Hot 100. You can sort the chart page by overall popularity, genre, web, international music and year-end charts.
Because the lists are online and fully interactive, you can listen to most chart selections with a Spotify or Rdio account. Each artist has a live link that takes you to an artist information page where you can get bios, news, articles, chart history, photos and videos.
In addition to Billboard's traditional chart categories, which are largely based upon terrestrial radio listening formats, Billboard.com has expanded the number of charts within each respective musical genre to represent all of today's modern listening formats. These include digital (music downloaded via services like iTunes), streaming (music via streaming services such as Spotify and Pandora) and airplay (music on traditional radio stations).
You can find lists of popular music from other sites such as Spin.com, iTunes and music blogs. Billboard is the oldest and most trusted industry standard for tracking progress of all popular music.