Popular Libraries

• https://github.com/johnezang/JSONKit - optimized for speed
• https://github.com/stig/json-framework/ - long history and widely used
• https://github.com/TouchCode/TouchJSON - parses NSData instead of NSString

Articles

• http://www.cocoanetics.com/2011/03/json-versus-plist-the-ultimate-showdown/
• http://stackoverflow.com/questions/4993118/json-library-for-iphone-installation
• http://stackoverflow.com/questions/286087/best-json-library-to-use-when-developing-an-iphone-application
• http://stackoverflow.com/questions/2256625/comparison-of-json-parser-for-objective-c-json-framework-yajl-touchjson-etc