Harvest - Simple time tracking, fast online invoicing, and powerful reporting software. Simplify employee timesheets and billing. Get started for free.

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.

tinyTimeSheet - A basic time sheet for Mac.

Pomodone - Pomodone is the easiest way to track your workflow using Pomodoro technique, on top of your current task management service.

Timebound - Deadlines done better