I love pincushions and have them all over my house. Pincushions have such a long and varied history, and there are too many designs to count.
I have a wonderful book called Pincushions written in 1974 by Averil Colby, which covers their history and includes many photographs.
One of the vintage pincushions in the book gave me an idea. It was was a velvet ball nestled in a pair of cockle shells. It was so sweet. That pincushion was like a siren song -- I have shoe boxes of shells that I collected over the years on Florida's Marco Island, where my parents lived, and now I know the perfect use for some of them.
For the example below I used a whelk that stands 5 inches tall, and the cushion itself is black silk velvet stuffed with polyester fiber fill. I cut an oblong shape of the velvet, sewed it nearly shut, filled it fairly firmly, and stitched it closed. I then bunched it up to fit snugly in the whelk's opening, and finally used hot glue to affix it.
EDITED: Here are two more for your viewing pleasure! The pincushion on the left is made with two scallop shells, and the fabric is some of my beloved Japanese chirimen fabric (which I've been saving for years -- I just couldn't bring myself to cut into it!). On the right is a cockle shell, and the fabric is Indian sari fabric in my absolute favoritist color, avocado green.
I challenge you to wander around your house and find something unique with which to make a pincushion!