Try This :
if (!IsPostBack)
{
FillDropDownList();
}
private void FillDropDownList()
{
DataSet ds = new DataSet();
SqlDataAdapter myda = new SqlDataAdapter("Select fileds FROM tablename", connection object);
myda.Fill(ds);
drop_category.DataSource = ds;
drop_category.DataValueField = "fileds";
drop_category.DataBind();
drop_category.Items.Insert(0, new ListItem("Select", "0"));
}
Hope this will help you. if not please post it.