The listbox specifically doesn't have the ability to add extra data...

The combobox, listview and most grids (as well as collections) DO have this ability.

Your choices are simple.

1. Use a listview that only has a single column.
2. Create a collection to match the listbox

Code:
Dim cList as New Collection

list1.additem "display"
cList.add "display", "keyvalue"


Sub list1_click()
  msgbox "Extra Information " & cList(list1.listindex).key
End Sub
You just have to make sure both the listbox and the collection are kept in sync