I'm not kidding when I say Penzu is the most realistic re-creation of paper I've seen on the Web. The service has a serious leg up on its pulp-born competition with a slick looking college-rule that holds all your thoughts (intelligent or not) and saves them to the cloud. When it comes time to print them, they'll come out just like they look like on the page, sans rulings of course.
One thing Penzu does a little better than other Web-based note takers is structure your docs like a diary, and stack each entry as its own page. You can hop back and forth between them with relative ease, and Penzu is smart enough to put the most-recently created docs on top. Also integrated are images, which you can upload from your computer at up to 5MB a pop. They'll sit in the margin and out of the way of the text. A simple mouse-over will let you see them in full resolution.
Up until a week ago I would have found this little service to have a nice leg up on Google Docs, which I usually use to jot down notes when I'm in meetings or interviews with start-ups. In those situations I'm usually not in need of Google's more advanced editing features, and want something that will simply retain my notes in case of hardware catastrophe.
However, if you're looking for some really basic necessities like indentation, hyperlinks, and a way to search through your past work, you might want to stick with one of the more complex tools like Gdocs or Zoho Writer.