Chrono Plus - Chrono Plus is a convenient task manager and time tracking tool with a host of handy features
FreelanceStation - Time tracking and Invoicing for Mac. Built for freelancers.
Timings 3 - Timings - Track worktime on your Mac. Compatible with GrandTotal invoicing software.
Qbserve - Freelance time tracking, invoicing, and productivity improvement
RescueTime - Time management software that shows you how you spend your time & provides tools to help you be more productive.
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.