We liked TeuxDeux when we first saw it because it worked like an online paper calendar. The basic but well-designed web app has improved a lot since then, making navigation easier, offering organising columns for your "Someday" tasks and an iPhone app.
Chief among the big improvements to TeuxDeux are the "fast forward" and calendar buttons on the side of your weekly task view. Click them and you zoom ahead an entire week, or pick a calendar frame to look onward to. The "Someday" section you add non-dated items to has also picked up column headings, so you can loosely organise the stuff you plan on getting to. Since we last peeked, too, there's now a $3.99 iPhone app that syncs up with your online TeuxDeux list.
TeuxDeux is a free web app to use and continues to be a smart to-do manager for anyone who doesn't need priorities, tags or any such devices — just a place to list their tasks, day by day.