nayldock,
Немного рефакторинга
<html>
<head>
</head>
<body>
foo <br>
<select name="mySelect" id="font">
<option>Consolas</option>
<option>Verdana</option>
<option>Courier new</option>
<option>Times new roman</option>
<option>Impact</option>
</select>
<script>
document.getElementById("font").onchange=function(){
document.body.style.fontFamily=this.value
}
</script>
</body>
</html>