I've tried a lot of handheld devices, task management programs, and calendar applications over the years in my quest to stay organized. The one I always come back to: pencil and paper (with Ta-da lists coming in a close second). If you've got a lot to do, the last thing you need is a task list application that adds to your workload by throwing menus, checkboxes, categories, and all kinds of metadata fields on top of each to-do.
If you like paper and simple lists, try my new daily to-do list app, YouDo.
Each day gets its own sheet. You can scroll through the week to take a peek at what's coming. Small vertical bars flank each day to give you an idea of how many previous and upcoming tasks you have.
Add new tasks inline: tap, type, reorder, delete from the same screen. No submenus to wander through, no extra seconds shaved off your day.
Bonus feature: Set the background to white and use the app as a flashlight in times of darkness.
Learn more at the product page.
If it's Jan 23rd, 2010, you may not see the app in the iTunes store. Tomorrow and onward, yes!