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.

Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.

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

Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.

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

Strikethru - Strikethru is a kind of to-do list notebook for managing work lists and staying updated with the important tasks.