I'm having lots of trouble setting up the RestKit API to my app. I wonder if there is any other good API to make RESTful apps? I've just followed lots of tutorials and the github directory of the RestKit API, but I just can't get it up and running. I've seen that Xcode 4 is having problems importing this API.
This is an old question, Nowadays, after 4 years in iOS development I use AFNetworking: https://github.com/AFNetworking/AFNetworking
It is quite simple to start, and can be installed using cocoapods.
I can suggest standard iOS classes such as NSURLConnection and NSJSONSerialization.
Here is a series of posts that explains how to use Blocks to asynchronously perform Http requests against a RESTful API: http://kerkermeister.net/series/ios-and-rest-http-connections/