Even if a car's battery is completely dead (or hanging on for dear life), it doesn't have to be thrown away. While it certainly won't pay for a new battery, there are a few spots where that old battery can make a few bucks.
Centers that recycle metal materials may offer a little money for used car batteries. Local recycling centers are a good place to start to find metal recyclers in the area.
More often than not, auto parts stores have battery recycling programs where used-up batteries can be deposited. While they may not offer cash, there's a good chance of receiving store credit (perfect for a replacement battery).
The best way to get rid of a used battery is often to open it up to a world of online bidders. EBay, for example, connects sellers with buyers looking for specific batteries--new, used, and even dead.