Toggl offers desktop plugin for online time tracking
Toggle Desktop is tightly integrated with Toggl's online service. On the one hand that means you can't use the desktop application if you haven't signed up for a free account online. On the other hand, it means you can easily choose from a list of tasks that you've already set up. And you can access your reports from any computer with a web browser. You can also use Toggl Desktop on multiple computers, safe in the knowledge that all of your hours will be logged and stored online.
The desktop program will start counting your time as soon as you hit a task. Just click the big red button to pause a task, or if you need to switch gears and work on something else, you can always hit another task. If you accidentally log a few seconds or hours that you didn't actually work, you can always edit or delete a task from the Toggl Desktop interface.