Though I have never been a client of theirs, I have several friends at a company called Extensis Group [ http://extensisgroup.com/
]. I believe they're an HR multi-vendor solution (i.e. HR, benefits, and payroll) but may be able to help depending on your needs. They can work with companies with as few as 2 employees. I believe their client roster includes many New York startups, potentially a few from NYTM.
Would it make sense for me to send an intro between you and my friend? Or would you like me to send you her contact info?
Anybody on this list work with them? Feel free to chime in on your experience....