Hummingbird or Grasshopper?

While deadheading our purple coneflowers last night (and never finishing it), these little guys were flying all around me, snacking on our Giant 4 O'Clocks and even the phlox. They hover while beating their wings just like a hummingbird, but don't appear to have any feathers or to be birds at all. There are crazy big flying grasshoppers around here, but these don't appear to be hoppers either.

Anyone know?

ETA: White-lined sphinx moth, Hyles lineata

Thanks Brian, Katie, and Eric!