I’ve recently started using an application called dabble db. Without gushing too much, I think it’s the best online application I’ve used, period. It’s right up there with google’s maps, reader and email. In fact, if google have any sense they’ll buy dabbledb right NOW since it’s so damned good. It’s making my life massively easier already just working with some pretty simple data.
The application itself is really a database, but the User Interface is superb. It presents a sort of spreadsheet interface but instead of being a spreadsheet under the hood it’s a full relational database. Upload a spreadsheet and get going, and before you know it you’re working with vastly more control and much more naturally than previously. If you work with a lot of spreadsheets you really have to check it out.