Nagmay

Adds a ‘QR’ button next to ‘Get Shortlink’ on published pages and posts.
Your authors can click it to print out a QR image and promote what they created. The QR code is created using the ‘shortlink’. The plugin uses the Google Charts API and (as the name applies) is stupid simple to set up and use!
Note: WP4.4 hid the ‘Get Shortlink’ button. This plugin will also unhide that button.
<h4>Options</h4>
There is one optional feature. It allows you to add arbitrary text to the end of the shortcode. This can be useful for tracking purposes.

Stupid Simple QR

Allow authors to easily print a QR code for each page/post.

Julian M.

Magn QR Code for WP is a WordPress plugin that helps you to add QR Code or 2D Quick Response code into WordPress posts.
This plugin uses Google Chart API to generate the 2D QR Code image and then you can embed it into WP posts using a shortcode.
[qrcode href=””]
or you can use this in your template:
If you want to see this plugin in action you can visit http://aplicaciones.org/

Stupid Simple QR vs Magn QR Code for WP