Gift certificate to a nice dinner at a favorite resturant or maybe a new one that they would enjoy. Of course, you didn't give many clues such as age, interests, proximity to you, price range for gift, etc.
Bob An investment in knowledge pays the best interest. -- Benjamin Franklin
Especially if your family is large and dispersed, a family photo at a photographer's studio is nice.
My wife set up one for her parent's at their 40th, and I set up one for my Mother's 70th birthday (would have been about her 50th had my father still been living.) All the kids got the chance to order copies as well, which all did.
We bought some 'art' of a place special to them and us. Thousand Island Lake in the Eastern Sierra, on the John Muir Trail. Beautiful photograph, beautiful spot. The site of our first family backpack, 25 years ago. It hangs in their entry hall.
hsv_climber wrote:The best gift that you can give to your parents is the time (it can be in a form of vacations / trip) that you can spend with them.
+1 You may also want to take advantage of this opportunity to film them. I did a bio of my folks (yes they were around before you were born) and they thanked me for immortalizing them. I had no idea it would mean so much to them.