I've done some of these, but I'm mostly brainstorming for ideas this year.

• Make him his favorite meal (my dad loves steak)
• Get something for him that he has had a hard time finding locally (like a type of cigar...)
• Get him his favorite snack (my dad's is kimchee and peanuts)
• Find something of his that is broken, and get it fixed. Like a computer, pocketwatch, glasses, or transmitter.
• Add to his collection (my dad collects pipes)
• If his favorite book or movie has a corresponding movie or book, find it!
• Try to get him an autograph of his favorite actor
• Sit and chat it up all day
• Take something like a personalizable childrens' book about a daddy and full it out as an adult. My dad keeps his in his office :)
• Get him something really cool for his car
• My dad loved his personalized parking sign - most mall vendors sell them
• Get him some 'manly' flowers: dark Calla Lilies, Tiger Lilies, and a few Hawaii'an ones look great in a plain, solid vase.
• If he is religious, get him a blessed artifact
• Make a photo-reel of your favorite photos together