Charles proxy (http://www.charlesproxy.com/) let you see all HTTP requests done by your flash application, and (contrary to other tools like Firebug), let you also see the content of the Flash Remoting calls (function and arguments).
To quote the site:
“Charles is especially useful for Adobe Flash developers as you can view the contents of LoadVariables, LoadMovie and XML loads. Charles also has native support for Flash Remoting (AMF0 and AMF3)”
Very useful!
