I've recently done a run-through of several good (online) options for iPhone ToDo list apps, which I hope may be helfpul for some. It's at:
http://justanotheriphoneblog.com/wordpress/2007/09/22/iphone-to-do-list-applications-some-good-choices/
http://justanotheriphoneblog.com/wordpress/2007/09/22/iphone-to-do-list-applications-some-good-choices/