I like giving my dad an "experience". Red Baloon website is great for those. You can also pick up great deals through Living Social and Groupon. The last one I bought for him is a flight simulator experience, where he gets to fly a commercial plane with a qualified pilot.
The kids and I made a picture book for my husband using all the great photos of him with the kids and from our adventures. We included special notes from the kids. It didn't take too long to put together and was very well priced to have printed from Snapfish. He loved it!