My choice would be [Guayadeque Music Player][3]

Guayadeque is included in Ubuntu repositories and can be installed through Ubuntu Software centre

[![Guayadeque Music Player][1]][1]  
<sub>(source: [ubuntu.com](http://screenshots.ubuntu.com/screenshots/g/guayadeque/5010_large.png))</sub>  




**Requested features**:

 - Guayadeque supports dynamic or static play lists.
 - Guayadeque comes with sys-try applet and have ability to change song
   from taskbar
 - Album covers can be downloaded manually or automatically
 - Guayadeque can import music from various sources including external
   media
 - OSD Notification when the song is changing

![Guayadeque task bar applet][2]

**Additional features**

 - Play mp3, ogg, flac, wma, mpc, mp4, ape, etc
 - Allow to catalogue your music using labels. Any track, artist or
   album can have as many labels you want
 - Suggest music using last.fm service
 - Allow to subscribe to podcasts and download all new episodes
   automatically or manually

List of features can be found [here][4]

[1]: https://i.sstatic.net/aNdfW.png
[2]: https://i.sstatic.net/oPr8k.png
 [3]: https://www.guayadeque.org/index.php?p=/
 [4]: https://web.archive.org/web/20140419015840/https://apps.ubuntu.com/cat/applications/quantal/guayadeque/