Inexpesive dock & charger for S3
I don't own this, so I'm not recommending it, but if you're interested in something like the Samsung cradle and extra battery charger, for a lot less money, this might be worth a look. $18.29 for quantity one, and it will work with a thin case.
For only $17.48 each when QTY 50+ purchased - CaseDuo Charge & Sync Dock + 2nd Battery Cradle for Samsung Galaxy S3 - Black | IR Active Shutter 3D Glasses
I've bought a few items from monoprice in the past, and found the quality of their stuff decent.