Vitalist is a great free ToDo application which allows you to create a wide variety of ToDo items, and has a very nice interface.

<a href="http://iphone.vitalist.com" target="_blank"><img src="http://www.modmyi.com/appimages/vitalist.png" border="0" height="320" width="320" /></a>

<a href="http://iphone.vitalist.com" title="http://iphone.vitalist.com" target="_blank">http://iphone.vitalist.com</a>