On-line calendars can make your life easier. They can be accessed from any location and you can set an option to e-mail yourself a certain number of days before your best friend's birthday so that you don't forget yet again!  Many calendars also integrate to-do lists and allow you to e-mail yourself with reminders.

30 Boxes - This is a traditional and basic calendar with different options for reminders. Special features include syncing birthdays from Facebook and a To Do list.   Works very well for simple tasks.

Google Calendar This one offers many more options including a breakdown by hour, view my month, etc.. You can also import specialized holiday lists which people post on the net (eg. U.S. or Canadian holidays). Also has either a pop-up or e-mail option for reminders.

Mozilla Sunbird - Offers day, week and month view and different ways to customize the look. Also has options for reminders. You can publish your calendar on your own website if you wish. There is a plugin to integrate it with Mozilla's Firebird e-mail client.

Other Calendars

Calendars.net

Yahoo Calendar

Timebridge - integrates with Outlook and several other calendar tools

Doodle - schedule an event - make a choice mix of calendar and polling

Planning Wiz - plan and layout

Assign-A-Day - calendars that let you manage classes and assignments