vertical align middle in <div>

It's simple: give the parent div this:

display: table;

and give the child div(s) this:

display: table-cell;
vertical-align: middle;

That's it!

.parent{
    display: table;
}
.child{
    display: table-cell;
    vertical-align: middle;
    padding-left: 20px;
}

<div class="parent">
    <div class="child">
        Test
    </div>
    <div class="child">
        Test Test Test <br/> Test Test Test
    </div>
    <div class="child">
        Test Test Test <br/> Test Test Test <br/> Test Test Test
    </div>
<div>

Old question but nowadays CSS3 makes vertical alignment really simple!

Just add to #abc the following css:

display:flex;
align-items:center;

Simple Demo

Original question demo updated

Simple Example:

.vertical-align-content {
  background-color:#f18c16;
  height:150px;
  display:flex;
  align-items:center;
  /* Uncomment next line to get horizontal align also */
  /* justify-content:center; */
}

<div class="vertical-align-content">
  Hodor!
</div>

You can use line-height: 50px;, you won't need vertical-align: middle; there.

Demo

The above will fail if you've multiple lines, so in that case you can wrap your text using span and than use display: table-cell; and display: table; along with vertical-align: middle;, also don't forget to use width: 100%; for #abc

Demo

#abc{
  font:Verdana, Geneva, sans-serif;
  font-size:18px;
  text-align:left;
  background-color:#0F0;
  height:50px;
  display: table;
  width: 100%;
}

#abc span {
  vertical-align:middle;
  display: table-cell;
}

Another solution I can think of here is to use transform property with translateY() where Y obviously stands for Y Axis. It's pretty straight forward... All you need to do is set the elements position to absolute and later position 50% from the top and translate from it's axis with negative -50%

div {
  height: 100px;
  width: 100px;
  background-color: tomato;
  position: relative;
}

p {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
}

Demo

Note that this won't be supported on older browsers, for example IE8, but you can make IE9 and other older browser versions of Chrome and Firefox by using -ms, -moz and -webkit prefixes respectively.

For more information on transform, you can refer here.

I found this solution by Sebastian Ekström. It's quick, dirty, and works really well. Even if you don't know the parent's height:

.element {
  position: relative;
  top: 50%;
  -webkit-transform: translateY(-50%);
  -ms-transform: translateY(-50%);
  transform: translateY(-50%);
}

Read the full article here.