Now, as you might imagine, there are going to be problems with this if you have protected DRM files, so I recommend TuneSync only for users who have DRM-free music. Which you have, right?
If you have MP3 or Ogg audio files, though, you are going to like TuneSync a lot. The over-the-air syncing takes place every 12 hours, without intervention, though you can start the sync at any time. This is something you will need to pay for, too. The free version only syncs 20 songs from your iTunes library. The premium version is $5.99--a dollar more than the AirSync add-on for doubleTwist.
It's a bit hard to compare doubleTwist and TuneSync, since their interfaces are so different (i.e., doubleTwist actually has an interface and TuneSync doesn't). If you like the set-it-and-forget-it idea of music synchronization, I would recommend spending the extra buck on TuneSync. If you are looking for a straight-up iTunes replacement, look no further than doubleTwist. Even without AirSync, it's a nice app to have for your Android phone.
Linux users should not feel left out of the Android music crowd. Banshee, an excellent music player for the Linux desktop, has integrated Android support.
You wouldn't think that this would be such a big deal, given that Android is based on Linux and desktop Linux well, is Linux, but until recently there was not a big push to get music management working. Banshee used to require a special hidden file pushed to the Android drive in order for it to recognize the music files on that drive. No longer: now it's just plug and play.
I would be remiss if I didn't mention one very viable music alternative for Android phones: streaming services such as Rhapsody.
With a monthly subscription, I have found Rhapsody and similar services to be indispensable on Android phones. That's because these services can be accessed on any device (yes, even iOS devices), so once I set up my playlists on one device, the playlist is available on all the others. This is the promise of iCloud, long reached by Android users.
While it is true I don't "own" the music, as long as I have connectivity, then I can access the music just as if I did own it. There's really no difference. For the few songs I want to have on the device no matter what the connection strength is, there is the option (on Rhapsody) to simply buy the songs and download them directly to my device.