string sQuery = "SELECT CountryID, CountryName FROM COUNTRY";
DataTable dtData = new DataTable();
SqlConnection oSQLConnection = new SqlConnection("sConString");
SqlCommand cmd = new SqlCommand(sQuery, oSQLConnection);
SqlDataAdapter da = new SqlDataAdapter(cmd);
oSQLConnection.Open();
da.Fill(dtData);
da.Dispose();
DropDownList1.DataSource = dtData;
DropDownList1.DataValueField = "CountryID";
DropDownList1.DataTextField = "CountryName";
DropDownList1.DataBind();