Growing up I was always a Daddy's girl. He was my hero and the cards I gave him were a reflection of that admiration. The covers of the ones I made as a child, and the ones I bought as I got older, were images that I felt suited him. They were depictions of golf and old cars, lakeshores and rustic cabins. The verse inside was always sentimental, always carefully considered to communicate my true feelings about the type of man and father he was to me.
My brother, on the other hand, wouldn't have dared to be so overtly affectionate. It wasn't the macho thing to do. So his cards to Dad were typically decorated with humorous images, the message inside respectful, but funny. They did manage to convey the feelings he wanted to express without being overly drippy.
So, if you are among the many who feel the best way to honour Dad is with a greeting personally created by you, whether you want to make him chuckle or feel warm and fuzzy, then here are some wonderful sites with images to get the project started.