So, what's wrong with iTunes? (or what more would you want?)
GTanaka: 1.  The biggest problem I say is its entirely closed nature.  I don't mean simply closed source -- I've used tools such as Mediamonkey for Windows and have been relatively satisfied -- but entirely closed to plugins or user developed support.  Specifically I refer to the inability to use/add anything to use FLAC, lyrics search, grabbing high quality album art ( a la allcdcovers.com ), social integration (mixtape, last.fm), 3rd party hardware syncing, and library visualization.  Each of these could be solvable if only Apple allowed some sort of plugin integration2. See suggestions above3. Not using mac.