We just hired a contractor for a project, and the pay is based on hours. I just wonder if there is any way (e.g. software, website, etc) to track/verify the actual amount of time he spends on working the project, so we don't end up paying more/less than we should. Many thanks.
While I'm sure there a number of good tracking tools, let's back up a second. Are you paying for number of hours, or work produced?
Going into hiring the contractor you should have had a budget of what you were willing to spend, and then the contractor, once presented with the work desired, should have given you an idea of how long it would take/cost (estimate). As long as his/her estimate is within your budget, then it doesn't matter how many hours they're working, as long as the work is being performed and delivered. If it takes them less time (but they still deliver as promised) then they get to keep more. If not, and it takes them longer than they anticipated, then it's on them and doesn't cost you anything for their mistake.
Paying by the hour presents two potential problems - one, they may be fast but sloppy. Two, they may be great but slow. Chances of getting great AND fast are probably slim. So shoot for 'smart' and use a budget and estimate, not simply hours.
The threat of being charged extra hours is always there, similar to shop lifting if you were a retailer. All you can do is deploy various types of controls to help mitigate. If your scope is known, well defined, and you predict few changes, then securing your contractor under a firm fixed price (FFP) agreement will remove all threat of erroneous hours. Your risks are limited to the schedule and quality under that scenario; however, you have to pay for the luxury of transferring the cost risk to your contractor. The price WILL be inflated to cover your contractor's risks and contingencies. It is almost certain that you will pay more under a FFP arrangement then under cost plus or T&M with some evidence of erroneous charging. So, consider that carefully.
If your scope is a bit ambiguous and you secure under T&M or cost plus, then you do have risk of erroneous charging but you also have control over who is doing what and when. If you have your own estimates of the work before you authorize a start, you can track and control progress against hours claimed and actual costs. When unfavorable variances start to accrue, you can intervene and correct the situation before the costs become out of hand. This includes the possibility of unearthing erroneous charges and removing the source. If your contractor or a select few of resources are constantly on the fat side of your estimates, you can ask why and intervene.
What you "should" pay is the agreed upon target dollars plus or minus a reasonable variance. But this does not come as a surprise. You should know way in advance using standard tracking and control methods like EV where you are and where you are headed.
Can't help with paying to much, but a good time tracker I am using is toggl.com. I really like it. As for making sure you are getting your money's worth, that will come down to having someone on your side that can evaluate what they are producing and deciding if what they are producing jibes with what it "should" take.
Also get firm estimates when possible and if they keep missing, maybe it's time to renegotiate.
"Verify" still will be big problem, but for tracker you can use (hosted or own installation) Anuko TimeTracker.
Another solution can be to create project on Assembla, select needed tools (in addition to Time Tools), f.e Tickets, Files, Scrum, Milestones... and perform most tasks of ALM in this project