If your iTunes library is stocked full of great songs you want to listen to without creating the perfect tracklisting, shuffling tracks or sitting chained to your PC then you might be interested in PhoneTunes. With an Apple iTunes interface the software collates a database of your entire music collection directly onto your mobile. So there's no slow connecting or browsing between phone and PC.
You can then choose the title of each song to be played, manage the tracklist, organise songs by album or artist, raise or lower the volume, skip back and forward through songs and stop or return to the library playlist. The program works by establishing a direct bond between your mobile and iTunes through a Bluetooth connection, WiFi, GPRS or 3G. The other alternative of course would be to just get an iPod. I've heard they're pretty good.