37Signals produces a line of products designed to help keep you organized. Basecamp is a great collaborative project management tool, with message posting, file management, to-do's, scheduling, etc, etc. Backpack is a similar product, although aimed more for personal use, while Ta-da List is a free task list application.
All three offer free versions and are web-based. They look and work great in any browser and have a lot of really useful functions for keeping track of both personal and business "stuff"