Radio Tray is a minimalistic radio player for Linux that runs in the systray (can also use an AppIndicator for Ubuntu). The application is very lightweight and straightforward to use and comes with notifications support, multimedia keys and a sleep timer.
A new RadioTray version was recently released with plugins support so if you're a Python developer, you can now easily create new RadioTray plugins (my only wish is a last.fm scrobbling plugin).
The new version also comes with read-only bookmark support, improved user interaction in bookmarks configuration dialog, moved various features to plugins (sleep timer, notifications, media shortcuts), a new history plugin and bug fixes.
Download Radio Tray (.deb and source files available)