I used this last night so I know it works! Papa Johns Pizza has started marketing through Facebook. If you "add them as a friend/fan" on Facebook, THIS WEEK, they will give you a code for a free medium cheese pizza with an online order! (You have to buy something else online, but it's not one of those "regular menu price" things where you still spend $15.
Go to Facebook (Register if you have never used facebook
Search Papa Johns (you'll know you're on the right one, the promo is on the page)
Add yourself as a fan
Check your inbox for a notification or message from Papa Johns shortly after, they will send you a message, it contains a place for you to enter your email address.
Then just check your email, you'll get your one time code.
Visit Papa John's online (Register if you have never used before)
Enter the code, and add something else.
You can actually order a "Create your own" 6 inch pan pizza for $3.49, and you'll get the free pizza. I opted to get some of their yummy parmesean breadsticks for $4.99. I also opted to pick it up, so I didn't have to worry about a minimum delivery charge. Keep in mind, if you're planning on getting pizza, it appears you can combine it with the other specials on their website, but if you just want to get a quick meal, pick something small and you'll score the free pizza!
(Note, on Facebook, it says "w/ online pizza purchase" but when you enter the code on the website, it just says online purchase, so you could order breadsticks, cheesesticks, dessert, etc!