Looking to unload your unloved gadgets for extra cash? I've got some new websites to share with you.

The New York Times  reports there's a site called Priceonomics.com that offers price trends for a variety of different product categories. For electronics, you pop in what you've got (be specific) and it will tell you the value.

As an example, Priceonomics reports that a used iPhone 4S is going for an average of $500 in good condition. (Buying it new costs roughly $700).

The site even goes the additional step of averaging prices it finds on the web and suggesting that if you're trying to sell your used iPhone 4S, an acceptable price range would be anywhere from $388 to $612.

Other sites that cater to specific resale markets include the following. These can all potentially be great ways to turn unloved electronics into cash:

• Swappa.com for Android devices
• Glyde.com for gadgets and games
• Gazelle.com for Apple products, plus Android, BlackBerry and other phones
• NewtonsHead.com for Apple products, even damaged iPhones
• BuyBackWorld.com or BuyMyTronics.com for all electronics
• NextWorth.com for phones, cameras, tablets and games