Do you use some reminder service like rememberthemilk.com? There are several excellent ones, and if you don’t use Firefox, they’ll do a good job for you.
However, I’ve just discovered an add-on for Firefox that does the job of keeping your to-dos and reminders/alarms constantly available on your browser. No calendar program needed. Very handy. It’s called ReminderFox and you can find it https://addons.mozilla.org/en-US/firefox/addon/1191/. You can receive alarms in your browser and by email. You can even create “quick alarms” that remind you to do something a short time later, such as “it’s 4:00 p.m. — call your manager about the report.”
It’s set by default to reside in the right corner of the status bar at the bottom of the browser window. Just click on it and a fairly sophisticated reminder and to-do program window pops open. It’s very easy and intuitive, but there’s lots of user info and training available on the developer’s Firefox page (here). And it is free, but the developers would be most grateful for a small donation.