Galactic Readiness can also be increased using the iPhone, iPod and iPad app called "Mass Effect 3 Datapad".
The app increases readiness at a slower rate than actually playing multiplayer, but providing you're willing to check into your i-gadget every hour or so, you can easily earn +10-15% readiness in every sector per day.
You need an online pass for the app to transfer data to your Mass Effect 3 game (thanks to mDoolin14 for the confirmation).
Edit 2: The app has been removed from the App Store, but can still be accessed online at http://social.bioware.com/n7hq/
Thanks again to mDoolin14.