You can see by the replies here that this is not such a simple question. First, you have to clarify if you mean Prussian, or all German states combined. Then you have to take into account the differences in awards between ranks. A Generalleutnant would have different awards than a Leutnant, because many of the orders came in multiple classes.
In the case of aviation recipients, they would have all been junior officers or non-commissioned officers. Junior officers between the rank of Leutnant and Hauptmann would generally receive the following Prussian decorations in sequential order:
Iron Cross, 2nd class
Iron Cross, 1st class
Hohenzollern House Order, Knight with swords
Orden Pour le Merite
After that, there were almost no examples of junior officers being decorated with any higher Prussian awards, other than von Richthofen. His Red Eagle Order, 3rd Class with crown and swords was considered a much higher class than anyone of his rank would ordinarily receive.
If there were other examples of less famous junior officers (maybe some U-boat recipients?) being decorated beyond the PlM, it would most likely have been the Red Eagle Order 4th class with swords, or the crown order 3rd or 4th class with swords, but the PlM outranked all of these in status. There is only one pilot I know of who received any of these awards:
Rudolf Windisch was given the Crown Order, 4th class with swords while still a non-commissioned officer. This was done at the order of Kaiser Wilhelm, who made an exception to the rules for a particular act of valor.
Tim