One thing I don't think anyone has mentioned, and a stupid mistake I've made in the past (especially when dynamically populating selects). jQuery's .val() won't work for a select input if there isn't an option with a value that matches the value supplied.
Here's a fiddle explaining -> http://jsfiddle.net/go164zmt/
<select id="example">
<option value="0">Test0</option>
<option value="1">Test1</option>
</select>
$("#example").val("0");
alert($("#example").val());
$("#example").val("1");
alert($("#example").val());
//doesn't exist
$("#example").val("2");
//and thus returns null
alert($("#example").val());