Greeting Card Companies often have opportunities for individuals to write, illustrate and submit photos on a freelance basis. Submission procedures vary among publishers. Take the time to check out each company and have an idea of what is unique about their products before you submit.
Here is a great resource to get you started. I highly recommend it: How to Write and Sell Greeting Cards, Bumper Stickers, T-Shirts and Other Fun Stuff
Below you will find several Greeting Card and Gift Companies who do take submissions:
Check out these great resources as well: