Zenefits is top of mind, growing fast and operating all over the U.S., which is incredible because they're only a few years old. All of their HR services are free, like tracking employee PTO, changing 401K contribution amounts etc. etc., but Zenefits also employs a small army of insurance brokers. If you use Zenefits you can continue using your current insurance broker for employee health care policies, but they can offer you a quote as well. That's where a big chunk of their revenue comes from, which is fine. Btw the CEO still serves as the Zenefits administrator for the company, which I think is really cool, but that's coming from a product guy. Anyway I researched this topic last month, hope it helps.
Warm regards,

Gregg M. Kennelly