I used to use sticky notes and random pages in random notebooks to keep my tasks organized. Half of them would end up lost or in the laundry. Thanks to RTM, I no longer have that option.
All of my tasks are organized by date and available both online and on the web.
Remember the Milk has apps available for iPhone, iPad, Android, Blackberry, Twitter, Gmail and more. See them all here.
I mostly use RTM on my computer, but occasionally I’ll dip into the mobile app to add a task or see what I have coming up. I also use RTM to keep a running list of things I “hope” to do one day (I just don’t assign them a date).
For $25 a year, you can get a pro account with more features (push reminders on your phone, unlimited mobile syncs, etc.).