How about Abdulrahman al-Awlaki or Samir Khan? I suppose they didn't even get the semblance of due process, just were at the wrong place at the wrong time.

EDIT: parent asked for a source for secret courts, the "disposition matrix" is just that, except it doesn't even involve the judicial branch only the executive and has resulted in the deaths of 3 Americans, one purposely and two 'accidentally' whether killing Americans on purpose or on accident is worse or better I'll leave as an exercise for the readers imagination.