TopTracker - Beautiful, free time tracking

Toggl - Toggl is an online time tracking tool. It features 1-click time tracking and helps you see where your time goes. Free and paid versions are available.

RescueTime - Time management software that shows you how you spend your time & provides tools to help you be more productive.

Time Doctor - Time Tracking and Time Management Software that is accurate and helps you to get a lot more done each day.

Hubstaff - Simple yet powerful employee work tracker with screenshots, timesheets, billing, in-depth reports, and more. Understand productivity issues and act on them.

timeBuzzer - timeBuzzer enables freelancers and project-driven teams to track their time at the touch of a button, understand where their time goes and create reports with just a few clicks.