No. 1: Give of yourself
The last idea is the gift of "you." Commit to spend an afternoon with dear old Dad. Take him to a baseball game, out for ice cream or for a walk. No matter what, he'll appreciate you setting aside time to spend with him.
Another way to personalize this day is in writing. How does your dad best communicate? How do you best communicate the way you feel? If writing sounds like good option, find a nice card -- or better yet, make one -- and fill it with memories of him, a top 10 list of why you love him or thank him for specific things he's done for you.
Remember, the more specific the better. It may be difficult for you, but this will mean the world to him and it's better than any tangible thing he could have received.
Make it the best Father's Day ever.