Bucketlist.org - Log and catalog all the stuff you want to accomplish before you expire.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
List Challenges - Earn points for your life experiences. Find lists that interest you, and mark off what you've done.
Remember The Milk - Remember The Milk is a task and time management application for mobile devices.
Life Listr - ***AS FEATURED BY APPLE***
Things - Things is an easy to use task manager.