Employment Agencies For Nurses??

Is there such thing as an employment agency for nurses? I have never heard of one and I know that in the corporate world there are hundreds. Usually a company looks through an employment agency first before taking on individual applicants, if they are a large organization...and I was wondering if this is the same in the medical world?

I am just about to start nursing school and am filled with curiousity upon time for the job hunt- so I am sorry if that sounds like a completely ignorant question.