http://getwifisync.com/
Works with the iPhone, iPod Touch and now the iPad. Only available through the Cydia Store (Jailbroken devices only) since Apple rejected it. $10 for all your devices. I've been using it a week or so on my iPhone and now on my iPad, works great. Just launch the app and it syncs back to my Mac over WiFi.
It will
not do a full-backup over WiFi but will sync apps, music, movies, data, etc. You can still hook it up to USB and sync that way as well (which will do a full-backup).
Works on the Mac and Windows.