This is particularly useful in mobile development where it is more user friendly to use the default select options menu than a customised JavaScript dropdown, which are often hard to select from on a handset.
select
{
background: url(../images/icon-dropdown.gif) no-repeat right 0;
border: 2px solid #0E5FE8;
-webkit-appearance: none;
-webkit-border-radius: 0;
appearance: none;
border-radius: 0;
padding: 2px 5px 2px 2px;
width: 150px;
}

What does each part do?
-webkit-appearance: none removes the default select look and feel
background adds the new icon for the drop down
adding padding to make the clickable area larger, which is helpful on mobile