iTunes Media Player
It can be used from any application you're working in, since the frame stays on top of other windows.
The interface is based on a horizontal frame, which is placed on the bottom part of the screen. Evidently, it requires iTunes to run in the background.
As far as media controls are concerned, you can pause and resume the current song, enable repeat mode, view and access playlist entries, adjust the volume level, as well as play the previous or next track.
You may also view the current artist and song name of the playing track, change the default background color and font type, as well as modify the layout mode. There are no other options available.
The small widget does not put a strain on system performance, as it runs on very low CPU and RAM. It has a good response time and works smoothly, without causing the operating system to hang, crash or pop up error dialogs. Unfortunately, the Yahoo! Widget Engine project was discontinued, so iTunes Media Player shall not be receiving further updates.