Setting a part's VCC slightly lower than board's supply voltage
Definately a resistive voltage divider.

Personally I would use one of the 20+ turn potentiometers, so that the voltage could be fine tuned if needed.

Remember that pots act just like voltage dividers, and they can be tuned to eliminate the error margin. However, be careful to pick a pot, with the correct resistance value so that the chip has all the energy it needs available to it, and so that there is not too much waisted energy from the divider its self.