http://ben.nyben.net/post_184/custom-styling-select-box

selectbox-style.js

$('select.bb-styled').each(function(){
  var title = $(this).attr('title');
  if( $('option:selected', this).val() != ''  ) title = $('option:selected',this).text();
  
  var idName = $(this).attr('id') + '_container';
  $(this).before('<div class="bb-styled-container" id="' + idName + '"></div>')
  $('#' + idName).append(this);
  
  $(this)
    .css({'opacity':0})
    .after('<span class="bb-styled">' + title + '</span>')
    .change(function(){
      val = $('option:selected',this).text();
      $(this).parent().find('span').text(val);
  })
});