Android - Android and iTunes
Yes, you can actually use DoubleTwist in combination with TuneSync (or TuneSync alone) to sync with iTunes although you are limited to songs that are not DRM'd by Apple.
You can also do it without any app on your phone with Notpod (Windows only).
The only drawbacks that I am aware with either of these are not being able to use DRM and people have reported some unreliability. The problem in general with syncing Android with iTunes is that it may work today but if Apple changes something in an update you may get locked out until someone comes up with another work around. If you are all Android now, I'd recommend on cutting iTunes out of the picture all together.
Edit: Here's a couple other options I've come across that are pretty awesome:
- Dazzboard
- iSyncr WiFi Add-On. You need an app and a desktop client. The app costs a little but the desktop software is free. This one seems like the coolest option so far.
Edit 2: I happened upon another app...
- Music WithMe: Syncs your phone iTunes over Wifi or 3G. It doesn't stream the music, it download it to your phone. Also, I don't think it can handle DRM'd tracks. It's little pricey at $15, especially with the currently less than stellar reviews, but it may be one to watch.
There is also Missing Sync for Android to sync your iTunes playlists (and associated files) to your phone.
It works pretty well.
Not that I am aware of, however you could try Double Twist for similar functionality.