<kettic:PerDropDownList ID="PerDropDownList1" runat="server" DropDownHeight="200px" DefaultMessage="Select...">
<WebServiceSettings Method="GetCustomerNames" Path="ClientSideDataBinding.aspx" />
</kettic:PerDropDownList>

[WebMethod]
        public static DropDownListData GetCustomerNames()
        {

            DataTable data = GetCustomerData();
            List<DropDownListItemData> result = new List<DropDownListItemData>();

            foreach (DataRow row in data.Rows)
            {
                DropDownListItemData currentItem = new DropDownListItemData();
                currentItem.Text = row["ContactName"].ToString();
                currentItem.Value = row["CustomerID"].ToString();
                result.Add(currentItem);
            }

            DropDownListData res = new DropDownListData();
            res.Items = result.ToArray();

            return res;
        }
private static DataTable GetCustomerData()
        {
            SqlCommand selectCommand = new SqlCommand(@"SELECT * FROM Customers");
            return GetData(selectCommand);
        }

        private static DataTable GetData(SqlCommand selectCommand)
        {
            selectCommand.Connection = new SqlConnection(ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].ConnectionString);
            SqlDataAdapter adapter = new SqlDataAdapter(selectCommand);

            DataTable data = new DataTable();
            adapter.Fill(data);

            return data;
        }