$.getJSON("http://jsonip.appspot.com?callback=?",function(data){
    alert( "Your ip: " + data.ip);
});

file.xml:

<?xml version="1.0" ?>
<result>
    <item>
        <id>1</id>
        <title>title1</title>
        <description>desc1</description>
    </item>
    <item>
        <id>2</id>
        <title>title2</title>
        <description>desc2</description>
    </item>
    <!-- ... -->
</result>

$.get('file.xml',{},function(data){
    $('item',data).each(function(){
        var $this       = $(this);
        var id             = $this.find('id').text();
        var title         = $this.find('title').text();
        var description = $this.find('description').text();
        //do something ...
    });
});

<div id="sites">
    <a id="site_1" href="http://siteA.com">siteA</a>
    <a id="site_2" href="http://siteB.com">siteB</a>
    <a id="site_3" href="http://siteB.com">siteC</a>
    ...
</div>

you need to get 1 from site_1, 2 from site_2 …

$("#sites a").click(function(){
    var $this     = $(this);
    var nmb     = $this.attr('id').match(/site_(\d+)/)[1];
    ...
});

<div id="result">12343778</div>

var delimiter = '.';
$('#result').html()
            .toString()
            .replace(new RegExp("(^\\d{"+($this.html().toString().length%3||-1)+"})(?=\\d{3})"),"$1" + delimiter)
            .replace(/(\d{3})(?=\d)/g,"$1" + delimiter);

var text = $("#textareaId").val();
var lines = text.split(/\r|\r\n|\n/);
alert(lines.length);

jQuery.fn.log = function (msg) {
    console.log("%s: %o", msg, this);
    return this;
};
$('#some_div').find('li.source > input:checkbox').log("sources to uncheck").removeAttr("checked");

// Based on: http://www.quirksmode.org/js/findpos.html
var getCumulativeOffset = function (obj) {
    var left, top;
    left = top = 0;
    if (obj.offsetParent) {
        do {
            left += obj.offsetLeft;
            top  += obj.offsetTop;
        } while (obj = obj.offsetParent);
    }
    return {
        x : left,
        y : top
    };
};

function isCreditCard( CC ){
    if (CC.length > 19)
        return (false);

    sum = 0; mul = 1; l = CC.length;
    for (i = 0; i < l; i++){
        digit = CC.substring(l-i-1,l-i);
        tproduct = parseInt(digit ,10)*mul;
        if (tproduct >= 10)
            sum += (tproduct % 10) + 1;
        else
            sum += tproduct;
        if (mul == 1)
            mul++;
        else
            mul–;
    }
    if ((sum % 10) == 0)
        return (true);
    else
        return (false);
}

$("#element").live('click', function(e) {
    if( (!$.browser.msie && e.button == 0) || ($.browser.msie && e.button == 1) ) {
        alert("Left Button");
    }
    else if(e.button == 2)
        alert("Right Button");
});

var img = $('#imageid');
var theImage = new Image();
theImage.src = img.attr("src");
alert("Width: " + theImage.width);
alert("Height: " + theImage.height);

$('#target div:not(#exclude)').hide();
//or
$('#target').children().filter(':not(#exclude)').hide();

$('element').bind('resize', function(){
alert( 'Height changed to' + $(this).height() );
}

$('someTableSelector').find('tr:gt(0)').remove();

1 level:
$('*:not(* *)');
2 level:
$('*:not(* *)').find('> *');
3 level:
$('*:not(* *)').find('> * > *');

var foundin = $('*:contains("some string bla bla")');

alert($(document).scrollTop());

$('* :not(.someclass)')

$('#myTable tr:last').after('<tr>...</tr>');

num = num.toString(16);
reverse process:
num = parseInt(num, 16);

var elements = $('#someid input[type=sometype][value=somevalue]').get();

var date = new Date();
date.setTime(date.getTime() + (x * 60 * 1000));
$.cookie('example', 'foo', { expires: date });

example: first 10 anchors
$('a').slice(0,10);
//or
$('a:lt(10)');

//Get the value of a selected option
$('selectElement').val();

//Get the text of a selected option
$('#selectElementId :selected').text();

//Remove an option (e.g. id=1)
$("#selectElementId option[value='1']").remove();

$(document).ready(function() {
    var dt = new Date();
    dt.setSeconds(dt.getSeconds() + 60);
    document.cookie = "cookietest=1; expires=" + dt.toGMTString();
    var cookiesEnabled = document.cookie.indexOf("cookietest=") != -1;
    if(!cookiesEnabled){
        //cookies are not enabled
    }
});

var tog = false; // or true if they are checked on load
$('a').click(function() {
    $("input[type=checkbox]").attr("checked",!tog);
    tog = !tog;
});

$("ul > li").click(function () {
    var index = $(this).prevAll().length;
});

$("#lda-form").submit(function(){
    var day = $("#day").val();
    var month = $("#month").val();
    var year = $("#year").val();
    var age = 18;
    var mydate = new Date();
    mydate.setFullYear(year, month-1, day);

    var currdate = new Date();
    currdate.setFullYear(currdate.getFullYear() - age);
    if ((currdate - mydate) < 0){
        alert("Sorry, only persons over the age of " + age + " may enter this site");
        return false;
    }
    return true;
});

if($(element).is(":visible")) {
    //The element is Visible
}

<div id="foo">
<div id="bar"></div>
<div id="baz">
<div id="biz">
</div>
<span><span>
</div>

//jQuery code to count child elements
$("#foo > div").length

jQuery.fn.center = function () {
    this.css("position","absolute");
    this.css("top", ( $(window).height() - this.height() ) / 2+$(window).scrollTop() + "px");
    this.css("left", ( $(window).width() - this.width() ) / 2+$(window).scrollLeft() + "px");
    return this;
}

//Use the above function as:
$(element).center();

$().ready(function() {
    $('#add').click(function() {
        !$('#select1 option:selected').appendTo('#select2');
    });
    $('#remove').click(function() {
        !$('#select2 option:selected').appendTo('#select1');
    });
});

$(document).ready(function(){
    $("#checkboxall").change(function(){
        var checked_status = this.checked;
        $("input[name=checkall]").attr("checked", checked_status);
    });

});

$(document).ready(function() {
    var pathname = window.location.pathname;
});

$(function() {
    $(document).keypress(function(e){
        switch(e.which){
        // "ENTER"
        case 13:
        alert('enter pressed');
        break;

        // "s"
        case 115:
        alert('s pressed');
        break;

        (...)

        }
    });

});

$(imageobj).attr('src', $(imageobj)
           .attr('src') + '?' + Math.random() );

var imgsrc = 'img/image1.png';
$('<img/>').load(function () {
    alert('image loaded');
}).error(function () {
    alert('error loading image');
}).attr('src', imgsrc);

var totalimages  = 10;
var loadedimages = 0;
$("<img/>").load(function() {
    ++loadedimages;
    if(loadedimages == totalimages){
        //All 10 images are loaded
    }
});

clearSelection      : function () {
    if(document.selection && document.selection.empty) {
        document.selection.empty();
    } else if(window.getSelection) {
        var sel = window.getSelection();
        sel.removeAllRanges();
    }
}
$(element).bind('dblclick',function(event){
    //do something
    clearSelection();
});

var email = 'info@tympanus.net'
if(!(/^((([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+(\.([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+)*)|((\x22)((((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(([\x01-\x08\x0b\x0c\x0e-\x1f\x7f]|\x21|[\x23-\x5b]|[\x5d-\x7e]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(\\([\x01-\x09\x0b\x0c\x0d-\x7f]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]))))*(((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(\x22)))@((([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.)+(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.?$/i.test(email)))
alert('Invalid Email');

<ul>
<li>cloud</li>
<li>sun</li>
<li>rain</li>
<li>snow</li>
</ul

var items = $('.to_order li').get();
items.sort(function(a,b){
    var keyA = $(a).text();
    var keyB = $(b).text();

    if (keyA < keyB) return -1;
    if (keyA > keyB) return 1;
    return 0;
});
var ul = $('.to_order');
$.each(items, function(i, li){
    ul.append(li);
});

timeout = setTimeout(function(){myFunction(param)},time);

$(document).ready(function(){
    $(document).bind("contextmenu",function(e){
        return false;
    });
});

$('imageelement').fadeOut(function() {
    $(this).load(function() {
        $(this).fadeIn();
    }).attr('src', AnotherSource);
});

//extend the jQuery functionality
$.extend($.expr[':'], {

    //name of your special selector
    moreThanAThousand : function (a){
        //Matching element
        return parseInt($(a).html()) > 1000;
    }
});

$(document).ready(function() {
    $('td:moreThanAThousand').css('background-color', '#ff0000');
});

var count = 0;
function myFunction() {
    count++;
    if(count > 5) clearInterval(timeout);
    //do something
}
var timeout = setInterval(myFunction, 20000);

if ($("#elementid").length) {
    //it does!
}

var req = $.ajax({
type:     "POST",
url:     "someurl",
data:     "id=1",
success: function(){
//something
}
});
//Cancel the Ajax Request
req.abort()