M.J.
Are you involved in any professional associations? Those are a great place to start. Most will have listings on their websites of recruiters in the industry. Some associations will endorse particular recruiters, too.
Also, ask around. Talk to others in your field and ask if they've used a recruiter before.
If all else fails, you can look online or in the phone book to locate ones serving your field. Then, contact them and get a sense of what you think. You can often get a good impression just by your initial interactions with a firm -- whether staff are friendly, whether your calls are returned promptly, etc.
Good luck!