We had to create a custom module for a client who wanted selectable options in the checkout review page which asks “How did you hear about our website?” with some options like Social Media, Blog, Search Engines etc. Basically this module creates a custom field in the checkout review section. This module can be pretty useful if you want to collect the information on how your customers ended up in the website or what source referred them. For developers this can be modified easily to achieve similar requirements. Download link at the end of this post.
Please check screenshots:
If you think this can be useful for you, please download it here: 2HatsLogicReferrer
Also find it here in gitHub – https://github.com/hatslogic/custom-checkout-field-magento/