Tudu is a dead simple to-do list that doesn't get in your way.
I built this for two reasons:
(1) to learn Rails, (2) to build a to-do list to my own liking (I've never found one that I liked)
Any suggestion or criticism is totally welcomed.
Suggestions: don't ask for an email address/password right from the get go, you can simply use a cookie for the first session, and ask people to sign up once they add a few entries. Then you associate their old entries with the newly created account. Also, give a reason why you need an email address, that's a huge barrier otherwise.
I've been toying around with todo lists as well lately, but you're much further along than I am. (I'm using the todo list concept as a way to try out various frameworks, never thought of actually releasing it to the public).
I like the very clean design and minimalist user interface.
By the way, my McAfee SiteAdvisor goes red when visiting your site.
Also, no way to delete my account.