getting your Library List on your phone/pda?

Have you ever bought a CD and discovered, once you got home, that you you already owned it? Embarrassingly, I have. Not infrequently, either. Now, I believe in supporting my local music store as much as the next guy, but that's a little bit ridiculous.

What I'd love is to have my music library metadata (not all of it, necessarily, but at least artist/album) on my iPhone, so I can see what I own, and what's missing, while prowling the racks at my neighborhood music store.

As long as I'm dreaming, it would be an easy sync operation, so it would stay current as my collection grows.

So as they say, is 'there an app for that?' Or perhaps some other technique that isn't too overly tweaky and manual?

Thank you for your help and experiences.
If you go to Google and at the top of the page, click on the "more"....that will open a list of categories. Click on the one that says Documents. From there you can create a spreadsheet where you can input all your music you have .
Look up for CDs. Great collector software and you can easily export data. You can also let them host your collection so you can browse it remotely. has been around for years and is very good. Main program runs on a PC or Mac. It can read a CD on your computers drive, scan barcodes or in the newest version read digital files from a hard drive or server and auto arrange them by album... very cool!

They have an optional iphone app that syncs with your main computer by WiFi and displays your collection on the iphone.

I've been using their Movie Collector and their Music Collector since 2002.... Don't Leave Home Without It!

Anyone use a scanner to catalog their library?