I hear some big company recently developed a spreadsheet, or something. If you enjoy spreadsheeting online though, check out Numbler. It's been around for a bit longer, and it's based off of some interesting technology I have heard about.
(Disclaimer: Numbler is not a product of Divmod, Inc. I have no
affiliation with Numbler other than I think Carl is kind of cool, athough I
wish he'd put some dang links on that page to the Athena site.)
Update: Carl added that link I mentioned to the "about" page. Thanks, Carl!