original from http://jsfiddle.net/charlescarver/XZE3x/

calendar.js

  	// Calendar
		function calendar(d) {

		    $("#calendar").remove();
		    $("#calendar_container").append("<table border='1' id='calendar'></table>");

		    t = new Date(d); // Today [Wed Jan 16 2013 00:00:00 GMT-0500 (EST)]
		    var d = t.getDate(); // Today's date (1-31) [16]
		    var y = t.getFullYear(); // Full year [2013]
		    var m = t.getMonth(); // Month (0-11) [0]
		    var mN = ["January", // Month name array (0-11)
		    "February",
		        "March",
		        "April",
		        "May",
		        "June",
		        "July",
		        "August",
		        "September",
		        "October",
		        "November",
		        "December"];
		    var fM = mN[m]; // Full month name [January]
		    var dIM = new Date(y, m + 1, 0).getDate(); // Number of days in current month (1-31) [31]
		    var dILM = new Date(y, m, 0).getDate(); // Number of days in last month (1-31) [31]
		    var dOW = new Date(y, m, 1).getDay(); // Day of the first day of the month (0-6) [2]
		    var nOW = Math.ceil((dIM + dOW) / 7); // Number of weeks in the month, including space [5]
		    var w = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];

		    function datDate(m, day, y) {
		        date = new Date(" " + mN[m] + " " + day + " " + y);
		        return date;
		    }

		    $("#calendar").append("<tr><td class='month' colspan='7'>" + mN[m] + " - " + y + "</td></tr>");

		    $("#calendar").append("<tr class='day'></tr>");
		    for (var i = 0; i < 7; i++) $(".day").append("<td>" + w[i][0] + "</td>");

		    if (m === 0) {
		        n_m = 12;
		    } else {
		        n_m = m - 1;
		    }
		    var pre = new Date(y - 1, n_m + 1, 0).getDate();
		    var daysInLastMonth = new Date(y, n_m + 1, 0).getDate();
		    var after = (7 * (nOW)) - (dOW + dIM);
		    var count = 0,
		        $row;
		    for (var i = 0 - dOW; i < dIM; i++) {
		        var day = i + 1;
		        if (count % 7 === 0) {
		            $row = $("<tr class='row'>").appendTo("#calendar");
		        }
		        if (day > 0) {
		            date = datDate(m, day, y);
		            if (day === d) {
		                $row.append("<td class='calendar_date current_date watch' data-date='" + date + "'>" + day + "</td>");
		            } else {
		                $row.append("<td class='calendar_date watch' data-date='" + date + "'>" + day + "</td>");
		            }
		        } else {
		            var day = daysInLastMonth--;
		            if (m === 0) {
		                var n_y = y - 1;
		                var n_m = 11
		            } else {
		                var n_m = m - 1;
		                var n_y = y;
		            }
		            var n_date = new Date(n_y, n_m, day);
		            $row.prepend("<td class='calendar_back watch' data-date='" + n_date + "'>" + day + "</td>");
		        }
		        count++;
		    }
		    for (var i = 0; i < after; i++) {
		        var day = (i + 1);
		        if (m === 12) {
		            var n_y = y + 1;
		            var n_m = 0
		        } else {
		            var n_m = m + 1;
		            var n_y = y;
		        }
		        var n_date = new Date(n_y, n_m, day);
		        $("td:last").after("<td class='calendar_next watch' data-date='" + n_date + "'>" + day + "</td>");
		    }

		}

		function calendarSetup() {

		    function changed(c) {
		        $(".current").text(c);
		        localStorage.setItem("date", c);
		        b_current = new Date(c);
		        b_year = b_current.getFullYear();
		        b_month = b_current.getMonth();
		        b_date = b_current.getDate();
		        b_daysInLastMonth = new Date(b_year, b_month, 1).getDate();
		    }
            

		    if (localStorage.getItem("date")) {
		        var now = localStorage.getItem("date");
		    } else {
                localStorage.setItem("date", new Date());
		        var now = new Date(); // "1 March 2013"
		    }

		    calendar(now);
		    changed(localStorage.getItem("date"));

		    b_current = new Date(now);
		    b_year = b_current.getFullYear();
		    b_month = b_current.getMonth();
		    b_date = b_current.getDate();
		    b_daysInLastMonth = new Date(b_year, b_month, 1).getDate();
		    b_monthNames = ["January",
		        "February",
		        "March",
		        "April",
		        "May",
		        "June",
		        "July",
		        "August",
		        "September",
		        "October",
		        "November",
		        "December"];

		    function move(a, b, c) {
		        if (b_month === a) {
		            var year = b_year + b;
		            var month = c;
		            a === 11 ? day = 1 : day = new Date(year, month + 1, 0).getDate();
		        } else {
		            var year = b_year;
		            var month = b_month + b;
		            a === 11 ? day = 1 : day = new Date(year, month + 1, 0).getDate();
		        }
		        var now = new Date(year, month, day);
		        calendar(now);
		        changed(now);
		    }

		    function step(a, b, c) {

		        var year = b_year;
		        var day = b_date + b;
		        var month = b_month;

		        var now = new Date(year, month, day);
		        calendar(now);
		        changed(now);
		    }

		    $(".watch").live("click", function () {
		        if ($(this).hasClass("back")) {
		            move(0, -1, 11);
		        }
		        if ($(this).hasClass("next")) {
		            move(11, 1, 0);
		        }
		        if ($(this).hasClass("calendar_back")) {
		            var now = $(this).data("date");
		            calendar(now);
		            changed(now);
		        }
		        if ($(this).hasClass("calendar_next")) {
		            var b_now = $(this).data("date");
		            calendar(b_now);
		            changed(b_now);
		        }
		        if ($(this).hasClass("calendar_date")) {
		            var b_now = $(this).data("date");
		            calendar(b_now);
		            changed(b_now);
		        }
		        if ($(this).hasClass("today")) {
		            var b_now = new Date();
		            calendar(b_now);
		            changed(b_now);
		        }
		    });

		    $(document).keydown(function (e) {
		        if (e.keyCode == 37) {
		            step(0, -1, 11);
		        }
		        if (e.keyCode == 39) {
		            step(11, 1, 1);
		        }
		    });

		}

		// Onload
		calendarSetup();