UPDATE [4/25/2016] Now better written and fully supported version with more options and abilities hosted at GitHub.jQRSS

I saw the Selected Answer by Nathan Strutz, however, the jQuery Plugin page link is still down and the home page for that site did not seem to load. I tried a few other solutions and found most of them to be, not only out-dated, but EASY! Thus I threw my hat out there and made my own plugin, and with the dead links here, this seems like a great place to submit an answer. If you're looking for this answer in 2012 (soon to b 2013) you may notice the frustration of dead links and old advice here as I did. Below is a link to my modern plugin example as well as the code to the plugin! Simply copy the code into a JS file & link it in your header like any other plugin. Use is EXTREMELY EZ!

jsFiddle

Plugin Code
_{2/9/2015 - made long overdue update to check for console before sending commands to it! Should help with older IE issues.}

(function($) {
    if (!$.jQRSS) { 
        $.extend({  
            jQRSS: function(rss, options, func) {
                if (arguments.length <= 0) return false;

                var str, obj, fun;
                for (i=0;i<arguments.length;i++) {
                    switch(typeof arguments[i]) {
                        case "string":
                            str = arguments[i];
                            break;
                        case "object":
                            obj = arguments[i];
                            break;
                        case "function":
                            fun = arguments[i];
                            break;
                    }
                }

                if (str == null || str == "") {
                    if (!obj['rss']) return false;
                    if (obj.rss == null || obj.rss == "") return false;
                }

                var o = $.extend(true, {}, $.jQRSS.defaults);

                if (typeof obj == "object") {
                    if ($.jQRSS.methods.getObjLength(obj) > 0) {
                        o = $.extend(true, o, obj);
                    }
                }

                if (str != "" && !o.rss) o.rss = str;
                o.rss = escape(o.rss);

                var gURL = $.jQRSS.props.gURL 
                    + $.jQRSS.props.type 
                    + "?v=" + $.jQRSS.props.ver
                    + "&q=" + o.rss
                    + "&callback=" + $.jQRSS.props.callback;

                var ajaxData = {
                        num: o.count,
                        output: o.output,
                    };

                if (o.historical) ajaxData.scoring = $.jQRSS.props.scoring;
                if (o.userip != null) ajaxData.scoring = o.userip;

                $.ajax({
                    url: gURL,
                    beforeSend: function (jqXHR, settings) { if (window['console']) { console.log(new Array(30).join('-'), "REQUESTING RSS XML", new Array(30).join('-')); console.log({ ajaxData: ajaxData, ajaxRequest: settings.url, jqXHR: jqXHR, settings: settings, options: o }); console.log(new Array(80).join('-')); } },
                    dataType: o.output != "xml" ? "json" : "xml",
                    data: ajaxData,
                    type: "GET",
                    xhrFields: { withCredentials: true },
                    error: function (jqXHR, textStatus, errorThrown) { return new Array("ERROR", { jqXHR: jqXHR, textStatus: textStatus, errorThrown: errorThrown } ); },
                    success: function (data, textStatus, jqXHR) {  
                        var f = data['responseData'] ? data.responseData['feed'] ? data.responseData.feed : null : null,
                            e = data['responseData'] ? data.responseData['feed'] ? data.responseData.feed['entries'] ? data.responseData.feed.entries : null : null : null
                        if (window['console']) {
                            console.log(new Array(30).join('-'), "SUCCESS", new Array(30).join('-'));
                            console.log({ data: data, textStatus: textStatus, jqXHR: jqXHR, feed: f, entries: e });
                            console.log(new Array(70).join('-'));
                        }

                        if (fun) {
                            return fun.call(this, data['responseData'] ? data.responseData['feed'] ? data.responseData.feed : data.responseData : null);
                        }
                        else {
                            return { data: data, textStatus: textStatus, jqXHR: jqXHR, feed: f, entries: e };
                        }
                    }
                });
            }
        });
        $.jQRSS.props = {
            callback: "?",
            gURL: "http://ajax.googleapis.com/ajax/services/feed/",
            scoring: "h",
            type: "load",
            ver: "1.0"
        };
        $.jQRSS.methods = {
            getObjLength: function(obj) {
                if (typeof obj != "object") return -1;
                var objLength = 0;
                $.each(obj, function(k, v) { objLength++; })
                return objLength;
            }
        };
        $.jQRSS.defaults = {
            count: "10", // max 100, -1 defaults 100
            historical: false,
            output: "json", // json, json_xml, xml
            rss: null,  //  url OR search term like "Official Google Blog"
            userip: null
        };
    }
})(jQuery);

USE

//  Param ORDER does not matter, however, you must have a link and a callback function
//  link can be passed as "rss" in options
//  $.jQRSS(linkORsearchString, callbackFunction, { options })

$.jQRSS('someUrl.xml', function(feed) { /* do work */ })

$.jQRSS(function(feed) { /* do work */ }, 'someUrl.xml', { count: 20 })

$.jQRSS('someUrl.xml', function(feed) { /* do work */ }, { count: 20 })

$.jQRSS({ count: 20, rss: 'someLink.xml' }, function(feed) { /* do work */ })

$.jQRSS('Search Words Here instead of a Link', function(feed) { /* do work */ }) // TODO: Needs fixing

Options

{
    count: // default is 10; max is 100. Setting to -1 defaults to 100
    historical: // default is false; a value of true instructs the system to return any additional historical entries that it might have in its cache. 
    output: // default is "json"; "json_xml" retuns json object with xmlString / "xml" returns the XML as String
    rss: // simply an alternate place to put news feed link or search terms
    userip: // as this uses Google API, I'll simply insert there comment on this:
        /*  Reference: https://developers.google.com/feed/v1/jsondevguide
            This argument supplies the IP address of the end-user on 
            whose behalf the request is being made. Google is less 
            likely to mistake requests for abuse when they include 
            userip. In choosing to utilize this parameter, please be 
            sure that you're in compliance with any local laws, 
            including any laws relating to disclosure of personal 
            information being sent.
        */
}