I use a modified version of Getting Things Done (GTD) with Remember The Milk (RTM). I started with a rather complicated system and then started removing complexity until I endede with a very simple system that meets all my demands.
I have two lists:
Daily is used for all tasks that are bound to a special day or deadline, I do not use priorities on this list, except on the rare occasion where there are a great number of tasks for the current day. This list is used to plan my day.
Someday is used to hold my tickler file and I use priorities and rarely dates here.
I use Milpon on my Ipod as client. I like it better than the rtm-app and is also the best tool to re-date a number of tasks fast.
Milpon has one problem though, sometimes it wont sync correctly and the cache needs to be deleted and all tasks redownloaded.