I have just started playing around with this free service at http://www.reqall.com
It is a web based reminder app that lets you and others send you schedule and reminder events. You can send and receive the reminders via email, text message, and instant messaging. You can customize the annoyance level that you want to live with.
If you are away from the office and the computer and remember something that needs to be done, you can send a text message via your phone, set an alarm, etc., and reQall will send you a reminder at a time and in a format that you have previously specified.
Check it out.