OGGPlay is a music player application, it supports every format that is supported by your phone (through so called MMF plugins), and also adds OGG support to other applications that supports MMF plugins. The user interface for this program is a lot better compared with standard music player (the standard music player leaves to many empty space).
This open source application is still in beta version, and hopefuly when it gets out from beta, someone can have it signed. This application was created by Leif H. Wilden, and by other contributors. You can download this application from http://symbianoggplay.sf.net.