Congratulations! How about a photobook of your milestones together as a couple? Not sure about Snapfish, but Shutterfly automatically creates a photobook once you've uploaded your pictures in an album. You can re-arrange the photos within pages if you like but if you uploaded them in the desired sequence, the work is done for you. Check the processing time so that it arrives in time for your anniversary!
Another idea, if someone can help you set up is a candlelit dinner and a movie. Could be as simple as takeout.