If you want the source code of an already loaded webview, you can get it like this:
NSString *yourHTMLSourceCodeString = [webView stringByEvaluatingJavaScriptFromString:@"document.body.innerHTML"];
Update: method above works most of the time. But I recently was in a situation where I needed all the code source, not just the body.
Here is a better way:
NSString *yourHTMLSourceCodeString = [webView stringByEvaluatingJavaScriptFromString:@"document.documentElement.outerHTML"];
(It won't reload the webview).