I just got the Galaxy S3 2 weeks ago and I had the same problem. Since then I got Juice Defender Ultimate. I didn't think that'd do anything, but it actually improved the battery life substantially. You can set it to limit your data or WIFI to 30 minute intervals from when your screen is off. You still get calls/texts, just not the constant syncing of emails, Facebook, etc. That, and reducing screen brightness, and using battery saver settings should show you some huge improvements.