Tudu Lists is an online application for managing todo lists. Tudu Lists is a very simple application, which you can start using in seconds, but with some advantages over your home-made Excel todo list. Tudu Lists is Web-based, and accessible from anywhere on the planet. It can be shared amongst people: you can share lists with your friends, family, or co-workers. Can be accessed with an RSS feed: if one of your shared lists is updated, your RSS aggregator will warn you.
Tudu Lists is completely free. Just register and start using it. Even Tudu Lists' source code is free.