What wire do I run to feed 120v driveway lights a total length of 500' from the switch?
Plug your scenario into a voltage drop calculator.

If the entire 60W (0.5A at 120V) load is at the end of the run (which it isn't, but makes the calculation simple - your actual results will be better), 14 AWG copper wire fed by 120V has only 1% voltage drop. If you go up to 300W (2.5A at 120V) the drop would be 5.26%, which is still fine.

You could run 12 AWG copper instead if you want the future flexibility to run a much larger lighting load, or to do something like adding receptacles at the posts. The price difference should be relatively small compared to your full project budget.