For my dh's birthday I picked him up a coffee when I dropped off the boys' in the morning , then brought it in to him in bed (he worked, so I took him in to work so he could sleep in a little bit), then the kids and I decorated the house while he was at work. I invited his brother, sil and the neighbors next door over for dinner as a surprise, we had his favorite dinner with spice cake. It was very low key. The little ones gave him balloons and a light to read his book in bed, and a travel mug from the dollar store. All the kids made him birthday cards. I am taking him to get a new backpack to take his stuff to work in. He didn't want anything really big. He said it was a great birthday.
If he has a Harley, maybe something for it, a new helmet, saddle bags??? You could have it cleaned for him. Or how about some sort of Harley collectible. My SO used to have these really cool collectable replica Harleys, well, until the cat knock them off of the shelf... bad cat,lol