However, both of them require you to be in front of a computer - you can supplement them with paper (and many people do), making hard copies of the tasks, and writing down new ones as the occur to you later.
I take a different approach. By using both gmail and google calendar, both of which have some rudimentary level of integration with my treo, the treo itself becomes my connection to my organization tools while I am away from computers.
Since gmail is also where I keep my todo list (see earlier blog entries), it is easy for me to add todo items simply by emailing them to myself using the +todo address from my treo. I can also check my current todo items, and of course my mail (there are instructions for mobile gmail here)
More interesting is the calendar interaction. Firstly, google calendar offers an SMS interface - this can ping you when an appointment is looming, but also (and not a lot of people know this) has a two way feature where you can add appointments too. The quick add rules apply, so you can use plain language to describe the appointment - like "Dinner with ralph tomorrow from 8pm to 10pm at Psychos" - just SMS this to the 48368 number (you will have to "connect" your mobile to google's services first - but if you get SMS reminders already you are there).
Google calendar has a plain HTML view available of your calendar from the calendar settings screen - it's right there next to the iCal and XML icons - by using the private one, and selecting the agenda view, you can take the resulting URL and put it into your treo as a bookmark. By using the bookmark you will get a nicely formatted agenda view of the next few days of appointments.
The integration is basic, but works. I never even sync my treo any more (well, except for addresses, but I tend to keep them on the treo anyway), the google mail and calendar integration are fine for everything else, and a lot less hassle. You do have to be connected to the internet with the treo to make it work, but if I am out of range of a connection, the chances are I am not wanting to get stuff done anyway...