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

Timer Tab - Online countdown timer, alarm clock, and stopwatch.

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.

Online timer - Online timer is a free and easy-to-use tool that comes with a very simple way to get done with measuring time and alarm.

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

Gestimer - For those little reminders during the day