Millhouse- That is a great idea. I think spending time together is really the best gift. Taking your dad to a terrific restaurant that serves his favorite food is also a nice touch.
There might be a new restaurant in town that he has always wanted to visit but never got a chance to. I think the gifts should be things that your father may want instead of a gift that is practical.
It should be memorable, so I usually shy away from giving gift cards even though many people love them.