One of the apps on the front page of my iPhone is Ultimate ToDo's, v 1.4. I use this little gem for my personal life, my college life, and in my work. Unlike some of my other apps, I've used this one for several months now, and I'm extremely happy with the product.
Here's how I use Toodledo:
I have Ultimate ToDo set up to synchronize with Toodledo on my Mac, and this is where I input most of my project information. I have folders set up for my personal life, my college life, and my work life. In each folder, I further organize them by categories such as my different classes at college or projects I am working on.
The tasks can then be sorted by due date, by category, by folder, by importance, or in a variety of other ways. I especially like how I can set up a project and list subtasks within the project. These subtasks can be viewed within the project itself or independently by due date. A very handy feature!
On my iPhone, I have the To Do app on my front page for easy access. When I open the app, I have it set to display my schedule, which is organized by date due. I can see at a glance what I need to work on next or if I have an appointment that I need to keep. As I complete my projects, I simply "check" it off by selecting the box next to the project.
I sync my iPhone to my Mac by selecting the "sync" feature at the bottom of the screen. It syncs very quickly even on 3G.
From the iphone To Do, I can add a new task almost as easy as on the Mac. I can even add a voice note to my task!
I can view my tasks in a variety of ways on my iPhone also. I often use the Contexts mode, which allows me to view my projects by context. I find this very handy since I am using it for personal use, college and work.
There are so many ways to use this app. I pay for the Pro-Subscription which is $14.95 per year. This adds more functionality to the app and is worth the price. I use the Subtask feature, the scheduler (which will use my task and priority information to suggest tasks to complete based on the time I have available), and the customizable booklets (which are downloaded as pdfs and can be printed as a hard-copy reference). There are lots of other features which I have yet to take advantage of, but will as I get to know the program.
I've tried lots of To-Do programs and apps, but this one suits my lifestyle and needs. Check it out - it might be just what you're looking for!