Anniversary gifts...

Soon my parent in-law will celebrating their 4oth wedding anniversary and we gonna throw them a surprise party at their mansion haha! At first we planned to have it at a restaurant actually at ruby Tuesday but sissy opted her plans instead celebrate it at my parent in-law's house with some invited friends. Since that time i probably just having our baby so i can't join with them if in the restaurant you know with a days old infant. So to make the long story short am busy looking online what kind of gifts i should give them i wanted to be unique but not too expensive because my in-law are pretty much can afford anything anyway, what matters most is the thought that counts. I am also looking for my sissy in-law because their 17th wedding anniversary is just a day before them. Hmmm.... i wonder what gifts husband and I will give to them?