Thanks for mentioning Plex. I'd fiddled with it a long time ago but either it wasn't full-featured then or I didn't realize what it was capable of. I installed it tonight, and am blown away by the fact that I suddenly have my entire music library available for streaming. The app for iPhone cost $4.99, and now I have all my music anytime I've got WiFi or cell service. I already had a Mac that was on the net full time with a static IP address, so this was pretty convenient.
I will say, Plex isn't without its problems. I had to trash preferences and application support files to get it to work at all. I'll probably never be able to use it for the TV shows I have on disk because I've used a different naming convention than the one and only naming convention Plex supports. Plex provides no way to turn subtitles on or off manually that I could discover. Plex won't play any of my iTunes videos; it just animates its little busy circle forever. Most annoyingly, since I primarily want it for music, it won't shuffle my playlists, nor will it let me slide the progress bar ahead in time, and most times I tap next it brings up a modal error dialog about not being able to refresh the play queue, whatever that means, that must be manually dismissed by tapping OK. So the more I exercise the app the less thrilled I am, but, still, all my music is online and can be listened to anywhere, which is pretty amazing.