For our youngest, we got him a limited edition print of his city of birth (he's lived away for 10 years) and had it framed. We also took him out to a fancy named restaurant in London, he was more impressed that we'd managed to book it than anything else!
For our eldest, he chose a foot high sculpture of a bear as he's always had a thing about bears and we happened to see this somewhere on our travels. We all went out to the local Indian restaurant on the day, again his choice.
Both presents/meals hit the spot perfectly.