So, what's wrong with iTunes? (or what more would you want?)
jquery: I know you didn't ask about Windows users, but assuming you are from Apple and have an ear there, please forward this message to the appropriate individual...With my fairly large, multi-gigabyte library, iTunes often takes minutes to respond to user input. Sometimes during syncing it can take up to 30 minutes to respond to my input. Please performance-profile iTunes before frustrated and contractually-obligated-to-use-iTunes iPhone users slap you with a class-action lawsuit.