I work in HR and the metrics route is the way to go! Line out for your boss exactly what you do (lots of times they really don't know)- in #s, and if your dept keeps tracks of what you're doing on a departmental basis, (how many ads others are filling, how many the dept is doing total a week/mos, etc.), include this as well as I think it will help to show your contribution in comparison to the salaried employees. Any special projects you've taken on? Anything you've really done a fabulous job on? Don't mention personal finances, even if you were living off food stamps, it doesn't mean you *deserve* a raise.

Is there a pay range for your job? Where are you in it? Is there a job description? Are you meeting your expectations or are you exceeding them? Are you doing a lot more than what others in your same position are doing? Start with this... then maybe go into your commitment to HR & to the company...if you've transferred a few times you might want to say why you're ready to stay where you are. Good luck! There are lots of good articles online on this type of thing, anywhere like Monster to the ERENetwork to SHRM.