Obsolete business cards usually go in the trash. However, they make amazing thought organizers. You can use them as flash cards to remember stuff. You can write Bible verses on them and tuck them in your pocket and purse. They are so comfy to flip around and stash places. However, my favorite is to write my priorities on them so that I can flip through and rearrange them as needed. It's like sorting a deck of cards according to the current circumstances. How many times have I rewritten my priority list as I realize something needs to come before something else? You rewrite and it's a mess and it's annoying and you give up and go do something else. But if you write them on these business cards, you can just keep flipping them back and forth. It's wonderful. And it's a great way to recycle.
I've also made reusable name tags with them by gluing a magnet to the printed side.