I'm getting fond of backpackit, a hosted service to manage to-do lists, reminders, arbitrary notes and appoinments. I needed a while to get used to the idea to leave these info on the internet only, with no local copy on my notebook - but it works fine :-)
Backpackit has a cool mail-in feature - you send a mail to your backpackit-page and you're done. Just put a token like "todo:" in the subject line and backpackit automatically inserts it at the right place.
You can selectively share certain pages or items with others - making backpackit a simple collaboration tool. Try out the writeboard facility for group authoring - quite fancy.
Backpackit is imho an brilliant example of Web 2.0 software - no installation, just browser-based, neat and functional UI, both free and commercial accounts available. By the way, its written in Ruby by 37Signals.
Only drawback (or is it a feature?): It works only online. You can get used to this, believe me!
PS: Mac-Users: Go for packrat, a small app wich uses the backpackit-web-service-API to enable offline usage...