AMPlayer is a module for playing Audio MPEG files. It currently supports MPEG 1.0, 2.0 and 2.5, layers I, II & III. Making a frontend is very easy, and the idea is that you make your own if you can. An example frontend is available.
These are the most recent binaries (version 1.39)
There is now also an unofficial build of 1.39 that reportedly works on the Iyonix. It was created by Peter Naulls:
The previous stable version (1.36) is available here:
A selection of Frequently Asked Questions (FAQ) can be found here. Please read these before sending us bug reports or we'll spend all or free time answering questions again and not getting any development done.
It's well worth you visiting the ESP Music website and picking up the latest copy of the SharedSound module. It's free and will enable lots of different applications to play sounds at the same time.
Another thing worth picking up is John Duffell's excellent !Stream application that allows access to Internet Radio stations using the Shoutcast protocol. It can be found here among other useful things.