It seems to me that a growing company likes yours could benefit from an HR package. Having insurance, vacation, company policy and other info automated is a huge time saver. Plus, most packages integrate with payroll services such as ADP and a bunch of recruiting services.
To help keep costs down, you may want to look at a Web-based HR application. You'd get all the HR features of applications used by the largest companies (and with 50 employees I'm sure you are running up against more and more of those issues all the time) but you don't need to make the capital investment in hardware and network infrastructure.
Employease
http://www.employease.com/ and Ultimate Software
http://www.ultimatesoftware.com/ are two of the better ones I'm familiar with. I think they both offer online demos.
--Dan