looking for a business management software

hi all,
I was wondering if anyone could recommend a good software for a small business in the service industry. We have over 200 outside vendors that perform close to 40 assessments daily (assessments run from 2 hrs to 6 hrs).
We are looking for software that can be installed on our server, need to be able to customize it, need multiple user accessibility, be able to do workorder entry, scheduling, invoicing and payroll.
We have looked at Service CEO and ESC, but wanted more options.
Thanks for all your help.
BB