Ask the first broker you contact for what he needs on an employee census in order to put together his recommendations for you--it's all very standard information, such as employees' age, sex, ZIP code, family vs. single coverage, etc. It isn't necessary to provide names on this census. The carriers use the data to determine how many of each category you will most likely be insuring so that they can quote rates on the different medical coverage plans that they offer. Most carriers offer a PPO, a POS, and many also offer high-deductible plans with a health savings plan option, and HMOs. So the broker should provide you with a spreadsheet showing the various plans and carrier choices available.
I recommend that you ask three brokers for their quotes and do a comparison between the spreadsheets they present to you. Ask plenty of questions and check references. Talk with clients that are a similar size to your company so that you know the kind of service the broker gives. The odds are that you will find the best plans and services using this methodology.