Print key value as a class along with the label for a list field? I have a node with a field which is a List (integer). I can print the value in node tpl with the following: 

&lt;?php print render($content['field_name']);  ?&gt;


However I also need to style each result differently. For instance one of the options is 'large' and I want to add a background image to every 'large' result. 

How can I do this? I was thinking if I could print the key value as a class along with the label the I could easily do the rest with CSS.
You should not actually want to do this in your node.tpl file. Drupal uses a system of (pre)processors to alter variables before they get rendered. That is where the logic should go.

Have a look at this topic that has a lot of explanation and references https://stackoverflow.com/questions/2383865/how-do-i-use-theme-preprocessor-functions-for-my-own-templates

Once you have your output ready you should be able to do the styling with CSS.