Google DFP Plugin
 

Looking at Google DFP for banner delivery and wondering what you guys use to inject the code on your site, is there an available plugin that would allow you to add the tags to the most common places like header, footer, left side of forum, right site, etc ?

You should be able to just insert the invocation code into your ad location templates.

For the side columns, just add a template module to your cms (or whatever you are using for sidebar content) that contains the invocation code.