CSS :not(:last-child):after selector - Stack Overflow

CSS :not(:last-child):after selector - Stack Overflow

or if you can use before, no need for last-child

li+li:before
{
  content: '| ';
}

Child and Sibling Selectors | CSS-Tricks

p + p { font-size: smaller; }  
/* Selects all paragraphs that follow another paragraph */

#title + ul { margin-top: 0; }  
/* Selects an unordered list that directly follows the element with ID title */

http://jsfiddle.net/ra5BK/