How to set the selected value of a (ajax) combobox with jquery
function VeriYaz(id) {
        $.ajax({
            type: "GET",
            url: "VeriAl.aspx",
            data: "id=" + id,
            async: false,
            success: function (data) {
                var urunler = data.split('|');
                document.getElementById('<%= cmbkategori.ClientID %>').value = stripHTML1(urunler[0]);}
        });
        }

$("#<%=DropDownList1.ClientID%>").val("1");

$("#<%=DropDownList1.ClientID%>").val(stripHTML1(urunler[0]));

$("#<%=DropDownList1.ClientID%> option:contains(" + stripHTML1(urunler[0]) + ")").attr("selected", "selected");

$find("<%=ComboBox1.ClientID%>").get_textBoxControl().value = stripHTML1(urunler[0]);