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.

Arjen Tienkamp

Automatically generates QR codes for your posts and pages.
After activating the plugin it automatically generates a QR (Quick Response) code for any post or page you want. These codes can be scanned by smartphones, and will point its browser to your wordpress website or blog.

Create QR Code

Automatically generates QR codes for your posts and pages.

Stupid Simple QR vs Create QR Code