I've used a plugin called HiFi (Header Injection Footer Injection) for quite some time. I loved it's simplicity and functionality. With WordPress version 3.5, that plugin suddenly stopped working and wasn't in the repository any more. So I found this one. It does essentially the same thing with even more bells and whistles. I love that it doesn't add any additional comments or other fluff to the code - just what you type in and nothing more! I can't express how much I appreciate that. I only have one complaint (this can be read as "feature request") about this plugin - I would love to see the ability to restrict it's use based on the role. For example, an administrator can use it, but an editor can not.