a ASPxComboBox in DevExpress is their DropDownList

<dx:ASPxComboBox ID="WhichEnvironment" ClientInstanceName="WhichEnvironment"
      runat="server" ToolTip="View Roles">
   <Items>
      <dx:ListEditItem Text="Quality Assurance" Value="3"></dx:ListEditItem>
      <dx:ListEditItem Text="Production" Value="1" Selected="True"></dx:ListEditItem>
   </Items>
   <ClientSideEvents SelectedIndexChanged="function(s, e) {
         ReportGrid.PerformCallback();
      }" />
</dx:ASPxComboBox>