Couponer is a free and brilliant WordPress plugin that will allow you to create printable coupons fast and easy and all you have to do to show them is to use this in any place that you want to show them like inside the post.php for example:

<?php if (function_exists(‘display_coupons’)) { display_coupons(); } ?>

the coupons have a print this coupon link next to them that after clicking on them it will be opened in another page and print menu will be shown.

Here is the demo site for it.

to install this WordPress plugin just go here and download it, upload and activate it and finally just put the code above anywhere you want to show the coupons. Also if you want you can change the link at the footer of the coupons.