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.

TopTracker - Beautiful, free time tracking

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

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.

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

Hyperlogs - Are you still using spreadsheets to keep track of time? Time Tracking has never been this easy.