Free program for things to do and reminder for Windows 7.
There's also another good software which works with several programs to act as a reminder for that particular program - "Gumnotes".
Attach Sticky Notes To Any Website Or Document with GumNotes -
google calendar has features like sms reminders and create even by sms.
so you can use it anywhere when you don't have your pc or net connection.
go to settings and select offline to use google calendar offline.
use this extension for a better experience :
Hello, you could try wieldy:
remember the milk
Windows Vista sidebar gadget for Remember The Milk
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Comparison of Online ‘To-Do List’ services
evernote should serve your purpose and its really good .
" Evernote makes it easy to remember things big and small from your notable life using your computer, phone, and the web."