What I used do was put my absolute favorites in matted frames & hang them on walls. I haven't done theat yets ince we moved into our house last year.
I also scrapbook so periodically I have DS & I go through what all is saved. We'll pick our favorites & then I make a collage of them in his scrapbook. And then his extra favorite ones, I do seperately. I have him write the date & a small story about the picture with all the deatils of the art...sortof like a journal entry.
I've also taken themed art (like for holidays) & had them laminated & we've used them as place mats. My kids loved that!
We take some of their art to an assisted living or nursing home. DS really loved seeing the elderly's smiles when he handed them art work, even though he didn't know them!

We use some of the art to make a simple art book that is given to the grandparents at Christmas. But really, it can be done at any special time. I just cut all the pages to the same size & then punch holes in one side & let the child run yarn through the holes. And then we write the date of when it was given & a brief note. The grandparents always love it!