Xnoise is basically a music player but it can also play videos, and unlike other Linux music players, it uses a tracklist centric design:
The tracklist is a list of video or music tracks that are played one by one without being removed (right side of window). This gives you the possibility to enqueue any track in any order, regardless if they are on the same album or not.
I didn't call it a "media player" because even though it can play both audio and video files, it seems to be designed more towards playing music. Xnoise can in fact play any audio / video format supported by Gstreamer and what I like about it is that in the hierarchy view you have both music and videos - so if you have some videos along with your music, you can play the videos too, something I've always been looking for in a music player (using VLC for playing music just doesn't feels right for me). And the way this is implemented seems just right - the videos are automatically added to a separate group so they don't get mixed with the music files.
And it's very lightweight too! It's true I didn't add too many music files while testing (around 300) but it only uses around 9,5 MB of RAM while playing a video!
Xnoise also comes with plugins support and even though it's still in its very early development stages, there are a few plugins available already: lyrics, Last.fm covers, notifications and mediawatcher (watches folders for changes).
Like I said, Xnoise is still very new so there might be bugs and also, there aren't too many features for now, but I love the very clean interface and the overall usability. Xnoise started on the right track, hopefully it will continue to improve but still keep its simplicity and clean interface.
Download Xnoise (Ubuntu .deb files included) | 64bit users can download Xnoise .deb file from HERE and the plugins from HERE. (thanks to CokiDVD!).
Update: there is now an Ubuntu PPA repository available for Xnoise (obviously, for both 32 and 64bit).
Many thanks to Ubuntu Tips for the heads up!