Besprizornik,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css"></style>
<script>
document.addEventListener('DOMContentLoaded', function() {
var d = new Date(), sel = document.querySelector('.day');
sel.value = ('0'+ d.getDate()).substr(-2);
});
</script>
</head>
<body>
<select class="day">
<option value="0">
</option>
<option value="01">
01
</option>
<option value="02">
02
</option>
<option value="03">
03
</option>
<option value="04">
04
</option>
<option value="05">
05
</option>
<option value="06">
06
</option>
<option value="07">
07
</option>
<option value="08">
08
</option>
<option value="09">
09
</option>
<option value="10">
10
</option>
<option value="11">
11
</option>
<option value="12">
12
</option>
<option value="13">
13
</option>
<option value="14">
14
</option>
<option value="15">
15
</option>
<option value="16">
16
</option>
<option value="17">
17
</option>
<option value="18">
18
</option>
<option value="19">
19
</option>
<option value="20">
20
</option>
<option value="21">
21
</option>
<option value="22">
22
</option>
<option value="23">
23
</option>
<option value="24" selected="selected">
24
</option>
<option value="25">
25
</option>
<option value="26">
26
</option>
<option value="27">
27
</option>
<option value="28">
28
</option>
<option value="29">
29
</option>
<option value="30">
30
</option>
<option value="31">
31
</option>
</select>
</body>
</html>