WalletStation

This plugin allows you to create code generators for Xbox Live codes, Amazon codes, Minecraft codes, etc. In order for a 
user to obtain a code, they must go to a url, that you provide, to obtain a password. Once they obtain a password, they enter 
it in the generator to get a code.
Lite Features 
-Create 1 generator.
-Create 10 codes.
-Create 3 URLs per code.
-URLs are randomized.
-Customize generator’s style.
-Generators can be added on posts or pages.
-Codes can only be accessed by one person at a time. A code becomes active once one of its URLs are accessed. If a password isn’t entered, the code becomes non-active in an hour.
-Once a password is entered, the code and its URLs are deleted.
Pro Features 
-Create unlimited generators.
-Create unlimited codes.
-Create unlimited URLs.
-URLs are randomized.
-Each generator has its own style.
-Generators can be added on posts or pages.
-Codes can only be accessed by one person at a time. A code becomes active once one of its URLs are accessed. If a password isn’t entered, the code becomes non-active in an hour.
-Once a password is entered, the code and its URLs are deleted.
<a href="http://walletstation.com/code-generator/" title="Get Code Generator Pro" rel="nofollow ugc">Get Code Generator Pro</a>

Code Generator Lite

Marco

This plugin will display a QR code in your sidebar which you can easily scan with your handphone or tablet and read later on the way home, to office or to school.

QR code generator

This plugin will display a QR code of the actually loaded page in your sidebar.

Code Generator Lite vs QR code generator