I have the exact same question, but my parent's anniversary is only a week away and I still haven't decided what to get.
We've done the family portraits for my Dad's 70th birthday a few years back (and my sister is in a different state anyway so couldn't come). We've also done the wedding photo for their 40th anniversary. Mum wears only her favourite watch she got years and years ago and Dad has one that is not very old, he doesn't wear any other jewelery at all, but I think he is getting Mum a necklace and earrings. They are going on an anniversary trip interstate a few days after their actual anniversary (for 10 days or so, not too long), I was thinking about something for that, but keep coming up blank!
Anyone have any extra ideas??