It was on my to do list to write a nice little web app to track my to do list. Fortunately, there is one already available at [voo2do]. No download, this is completely web-hosted, meaning that data resides on somebody else’s servers. Simple with nifty features.
Of course, use the standard precautions when your data is being hosted on servers not in your direct control- don’t use it to keep track of your secret evil to-do list, don’t put sensitive or crucial data to which you must have 24×7 access, don’t plan on it being free forever (though it currently is free).
Update: 2/28 Well, site seems to be down. See the caution above about the need to have constant uninterupted access to your data.