It might sound like a slightly strange concept but KavaTunes allows you to create websites that browse in the same Coverflow style as iTunes.
KavaTunes helps you create interactive websites that look and work just like iTunes, enabling you to browse, search and play all of your music. Websites created in KavaTunes websites can stream your favorite playlists with continuous playback and even album artwork using your Mac as a web server.
If you don't want to use KavaTunes for anything else, why not just use it to populate the remaining gaps in your album cover collection in iTunes. Uploading your music can take a long time though, and much will depend on your internet connection and size of your music library.
The functionality of KavaTunes can be very hit and miss, however. You may experience several instability issues and find that creating Smartlists doesn't work very well. The program has recently been updated though and some of these problems seem to have been ironed out.
KavaTunes is an interesting application that brings the web and iTunes much closer.