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I've created a sample for you consisting of an index.htm and a system.cfc

Index.htm

<html>
    <head>
        <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js"></script>
        <script>
            $(document).ready(function(){
                $(".getData").click( function(){
                    var method = $(this).attr("method");
                    $.getJSON( "system.cfc?method="+method,
                        function(data) {
                        $("#res").val( data.server_name )
                    });
                });
            });
        </script>
    </head>
    <body>
        <textarea style="height:200px;width:200px;" id="res"></textarea>
        <input type="button" class="getData" method="getCgi1" value="Get Json 1" />
        <input type="button" class="getData" method="getCgi2" value="Get Json 2" />
        <input type="button" class="getData" method="getCgi3" value="Get Json 3" />
    </body>
</html>

system.cfc
<cfcomponent>
    <cffunction name="getCgi1" access="remote" returnFormat="json" output="false">
        <cfreturn cgi />
    </cffunction>

    <cffunction name="getCgi2" access="remote" returnFormat="plain" output="false">
        <cfreturn serializeJSON(cgi) />
    </cffunction>

    <cffunction name="getCgi3" access="remote" returnFormat="plain" output="false">

        <cfset var customCgi = '{"server_name": "#cgi.server_name#","server_port": "#cgi.server_post#"}' />

        <cfreturn customCgi />
    </cffunction>

</cfcomponent>