One of my favorite software companies (realmacsoftware) recently releaed a task app for the iPhone. The app has received a lot of press and positive reviews as the developers took a fresh look at new ways to interact with your iPhone to manage your "to do" lists.
Take a look at the video and you will see why people are so excited about it.
It is available in the Apple app store for $1.99. I have tried it out and the interface is really well though out and very fast. It is fantastic as a simple and personal list manager. It does not yet have functionality for higher level task management (things like project management or ability to implement GTD functionality or do searches or sorts) or sharing or delegations. However, most people don't want or need those functions, so if you are looking for a fast and fun list manager... you should definitely take a look at Clear.