http://www.myth-weavers.com/forumhome.php
Mythweavers is pretty excellent, though there are a handful of things I don't love about their sheet. It's not super automated, but it can handle a few things and won't get in your way if you're putting custom values into fields. It won't do anything really in the way of error checking though.
On the plus side it's free, keeps your sheet online and available from anywhere, looks pretty, and it is very easy to use.