iPhone library

ASIHttpRequest Rest Request library:

http://allseeing-i.com/ASIHTTPRequest/

ASIHTTPRequest vs NSURLConnection:

http://stackoverflow.com/questions/4035451/asihttprequest-vs-nsurlconnection

http://allseeing-i.com/ASIHTTPRequest-1.5

URL Loading System Programming Guide

http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/URLLoadingSystem/URLLoadingSystem.html

JSON parser:
JSONKit (currently fastest):

https://github.com/johnezang/JSONKit

http://www.building43.com/blogs/2010/05/28/reading-rss-feeds-on-iphoneipad-with-asihttprequest-and-cocoa-rss/