Android/Windows: Keeping music synced between your Android phone and Windows system has probably never been this easy. Install Winamp on both platforms, click your phone, and you can beam and receive music over Wi-Fi from your music collection, wherever it's stored.
Winamp itself does a pretty good job of importing music libraries from iTunes or Windows Media Player, and can also watch individual folders on your system for new files and changes. Once its set up, you install Winamp on your Android system and enable wireless sync in its settings. Back at the desktop, click on the Devices menu, and if your Windows system and Android are on the same Wi-Fi network, they should find each other pretty quick. Click to connect, approve the connection on your Android and (whew) you're connected.
Once you're hooked up between the two, you can set up bulk transfers to and from your device, pick out playlists that should always stay synced, fill your device's free space with podcasts or filler music, set the specific encoding for files transferred to the phone, and geek out to your heart's content. Right-click on the device and hit "Preferences" to get at everything, including settings for automatically syncing every so many hours, or after X hours without a good sync. Winamp also supports USB cable syncing, and it seems a bit faster, as you might imagine.
There are, of course, other solutions for syncing your Android to your music library, doubleTwist included. But Winamp is a pretty good player on the desktop, and a neat media player on the Android itself, so it seems worth the transition and learning curve if wireless syncing is something you want. It's a free download for Android phones, and requires the Windows software to sync.