I bought an art canvas...gave my boys acrylic paints and told them to paint a Disney scene (my boys are very young so it looked very "abstract"...we attached all of the pins they have collected over the past few vacations starting at the outside and working in over the years. That way we have something to look in the blank middle and it also gives us a way to easily see the "trends" in their collecting (my middle son had one year that he was in LOVE with Dumbo and almost every pin he traded for that year had something to do with Dumbo) and is a way to keep the whole collection together. Good luck...no matter how you end up showing them off they will bring a smile when you walk by!
I've framed some, I have a mat cutter and that really helps. I don't have any pictures of the ones I've done. Need to work out a way to take a pic without the glass glare.
My 11yo DD has been collecting Stitch pins and I think we are going to pin them to the black comforter that is her window covering. It will be a good backdrop and give it some decoration. She has a couple of shelves of stuffed Stitch's also so it will work in the room.
You can get big, thick unframed sheets of cork, used above from industrial supply places.
I found a large cork board from the Container Store (3'x2' or so) cheaper than Staples and office depot. One room of the house we moved into, was covered in cork.. I covered it in black fabric and stuck pins in it!