JSON2Apex is an online tool to convert JSON into Apex class. The URL is: JSON2Apex
This tool is hosted in Heroku.

This app allows a user to paste a JSON String, and then this app will generate strongly typed apex code that can deserialize it. This entire app is written in Java using Play framework.

A special thanks to superfell and metadaddy for providing this amazing tool.
Guys, please use this one while working with JSON and Apex code.