Ive used Remember the Milk for many years. Theyve now added a sub task feature which is a really nice addition. The app is great and syncs to data on their web application. You can also use Siri to add tasks to the app, making it easy to add tasks on the go. Remember the Milk is highly configurable using tags and smart lists, so you can design the interface the way you want it. Check out the online user forum on their website for lots of great tips and tricks.
kysusan about Remember The Milk: To-Do List, v4.0.43