Script

(function($){

    // Extend the jQuery fn namespace
    $.fn.extend({
        // RSS2Render
        rss2render: function(options) {
            // 今回使う変数たち
            var self = $(this),
                c = $.extend({
                    url: null,
                    number: 10
                },options || {});

            // URLがなければ処理を終了する
            if( !c.url ) {
                return false;
            }

            // loading文字列とRSSを一覧で表示するためのul要素を入れておく
            self.append(
                '<div id="loading">loading...</div>',
                '<ul/>'
            );
            
            // RSSの取得
            $.ajax({
                // 読み込むデータはXML
                dataType: 'xml',
                // 読み込みデータのURL
                url: c.url,
                // Ajaxの通信が成功した場合
                success: function(data) {
                    // loading文字列を消去
                    $('#loading', self).remove();
                    
                    // RSSにitem要素がひとつもなかった場合
                    if( $('item', data).length<1 ) {
                        $('ul', self).append('<li>記事がありません。</li>');
                        return false;
                    }
                    
                    // item毎に･･･
                    $('item', data).each(function(i) {
                        // 指定した数を超えた場合は終了する
                        if( i > (c.number - 1) ) {
                            return false;
                        }
                        
                        // itemの中のlinkとtitleを抜き出してulに追加する
                        var item = $(this);
                        $('ul', self).append(
                            $('<li/>').append(
                                $('<a/>', {
                                    href: $('link', item).text(),
                                    text: $('title', item).text()
                                })
                            )
                        );
                    });
                }
            });
        }
    });

})(jQuery);

jQuery(function($){
    
    $('#rss').rss2render({
        url: 'feed/rss2.xml',
        number: 5
    });

});

Demo