You can get a gift (like a picture frame, shirt) that has the word daddy on it. I like to bake, so I like to make a yummy goodie and write something on it like you are a daddy. With ds I did something really simple, and I told dh I had a surprise for him. (We often by little gifts for one another, so he was not suspicious.) I wrapped up the pregnancy test, and gave it to him. He was so surprised. I just showed him the test in my second pregnancy. This time I took the test before he woke up, so I pulled him out of bed. We tip-toed into the bathroom trying not to wake up our house guests. We had been trying for a year, and I could not keep it from him for a second.
Hopefully you will get better ideas from other people.