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

If it's a problem with the not selector, you can set all of them and override the last one

li:after
{
  content: ' |';
}
li:last-child:after
{
  content: '';
}

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

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

Every things seems correct. You might want to use the following css selector instead of what you used.

ul > li:not(:last-child):after

Your example as written works perfectly in Chrome 11 for me. Perhaps your browser just doesn't support the :not() selector?

You may need to use JavaScript or similar to accomplish this cross-browser. jQuery implements :not() in its selector API.