Cog is a great little audio player. Sadly enough development came to a halt about a year ago, but Dmitry Promsky gladly picked up this open source project to revive it and make it even better. Seeing what he was doing and the popularity this little player still has I offered to contribute too and redesign the User Interface and help with Interaction Design.
At the moment this is still a work in progress, but if you love simple to use, non-bloated little apps, then keep an eye on this project, or help us make it better with suggestions or by contributing to the project
Update (2015-03): Glad to announce that I am working on Cog Two. We are aiming at a release just after summer. Keep an eye out for it!