I have my own system for to-dos, based very much on the GTD system. What I do is I use a system of emails to send myself reminders. I have a gmail account devoted solely to GTD, and I can send myself To-dos from anywhere where I have access to the internet due to gmail's excellent online interface. I use a combination of
Mailtags and
Mail Act-On to process everything on my home computer. Mailtags and Mail Act-On provide a fast way to quickly tag my To-Dos, putting them in catagories such as things I can do "@home", or "@campus", or "@phone". I then use smart folders set to search for these tags. As a result I have very useful, self updating folders for everything I can be doing at home, or all the phone calls I need to make etc.
My system works well, although, it can be a little buggy. Mailtags crashes mail on occasion. You could say I'm looking forward to Leopard and the built in To-Do functions.