I collect paper. Big surprise.
I collect stamps. And make them too.
I collect turtles. Ceramic, glass, silver, crystal, fabric, stone. You name it!
I collect books. All my shelves have a row of books on them.
I collect postcards. Great to pick up while traveling.
And now I'm a member of Postcrossing.
I collect molas. They are my favorite pieces of textile art.
I collect ribbon. Can't buy just one roll - they're so inexpensive and colorful.
I'm sure there's more I collect, like different kinds of art supplies, but this is what quickly came to mind.
See other lists at Aimee's blog, artsyville