while (reader.Read())
{
    DropDownList1.Items.Insert(i, new ListItem(reader["Text"].ToString(), reader["Valye"].ToString(), true));
    i++;
}

DataTable source = new DataTable();

List<myClass> source = new List<myClass>();

DropDownList1.DataSource = source;
DropDownList1.DataTextField = "Text";
DropDownList1.DataValueField = "Value";
DropDownList1.DataBind();

SqlDataSource source = new SqlDataSource();
source.SelectCommand = "SELECT * FROM yourTable";
source.ConnectionString = Common.connectionString;

DropDownList1.DataSource = source;
DropDownList1.DataTextField = "Text";
DropDownList1.DataValueField = "Value";
DropDownList1.DataBind();