One of the keys to getting your thinks done it making sure that all of your "things" are written down in one place. Many people end up using slips of paper, emails, envelops and all sorts of artifacts to act as reminders of things that need to be done. Worst of all, some people just try to remember everything.
If you're looking for an online task-list application, you may want to check out Toodledo, which is pretty feature packed. Features include:
- integration with Google Calendar, Google Personal Homepage, Firefox, and IMified
- printable tasklist
- email alerts for your top tasks (called a hotlist)
- ability to import/export tasks to iCal, Palm OS, XML, CSV, and text.
- publishing of task lists to the web
They offer a pretty thorough features comparison here.