iTunes isn't a one-player jukebox
Apple's iTunes and iPod were made for each other. But that doesn't mean that the Mac version of iTunes is a faithful partner. The jukebox can natively interface with a few "proletarian" MP3 players, and with the help of various manufacturer plug-ins, it can cozy up with many more. This means that you can connect a player such as Creative's MuVo, and it will appear under the Source column in iTunes so that you can drag and drop MP3 and WAV files--sorry, no AAC--to and fro the player within iTunes. Of course, iTunes reserves its true love (that is, protected AAC files downloaded from iTunes Music Store) for the iPod only. If you're an iTunes fan who wants to use an MP3 player other than the iPod, check out these candidates, some of which require a Mac-only iTunes plug-in.