No one mentioned about Time Doctor?
I use that time tracking software alongside my team of VAs, designers and other freelance workers.
It works really well for tracking our work hours and monitoring our computer activity. Productivity at its best. :)
If I think back, we have nearly used around 7 different tools in the past 6 years, but we were unsatisfied with most of it, except the one that we have been using now for couple of years. The tool is time billing tool from Replicon.