It's brand new technology, but I think .mp3 (MPEG level 3) files are promising. You're supposed to be able to get around 10:1 compression ratio with no audible loss of fidelity. The encoding takes a lot of computational power, the things I've seen recommend a 166 MHz Pentium at least. I don't seem to have kept a book mark to any of the web pages that discuss it, but there was a thread on this subject a few weeks ago in this forum, and you should be able to find more information by finding the thread (do a forum body search).