When I was between jobs, I signed with Adecco. They are a very good company to work for, and place their employees in excellent positions. My first job with Adecco was temping at DuPont, and I loved it.
With a temp agency, everything you do is through them ~ you fax your timesheet to them every week, they send you a paycheck (not the company you're temping for), and if you have to miss work for any reason, you call your Adecco contact. I found it very easy to communicate with them, and enjoyed my time as a temp.