Alla963,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
</head>
<body>
<form onsubmit="return false">
<select id="select_">
<option value="one">1</option>
<option value="two">2</option>
<option value="three">3</option>
</select>
<input type="submit" value="Отправить" onclick="getValue()">
</form>
<script>
function getValue() {
var select = document.getElementById("select_");
var value = select.value;
alert(value);
}
</script>
</body>
</html>