These free anniversary cards do work for any anniversary, click on the link and you will be taken to a pdf to print at home. Try not to print them off on the normal fairly cheap printer paper you have for everyday stuff, otherwise it looks cheap and a very last minute decision.
You could print them out and then add to the design by attaching a photo that you love of the two of you. Or you could cut out the design and stick it to some card. Or a very sweet and fun idea is to print out every single one of them and have them hanging around the house or tucked into their bag. See if you can get a card on their desk at work, along with a flower as well! Think of it like the old Black Magic chocolate adverts where the line was "all because the lady loved ...". Nothing like a bit of daring to add to the romance of the day!