You should try WorkHack.com, it is a todo list compatible with IE and firefox.
Also, some extras that Stuff To Do has:
* Groups - share tasks with other people in your work group with simple drag/drop.
* Time tracking. Keep track of how much time you've spent on each thing.
* Reports. No fancy graphs, yet, but it does break things down by day and task over preselected time periods.
I recommend reading the whole book Getting Real (free from 37signals) especially chapter 5 on feature selection.
I recommend reading the whole book Getting Real (free from 37signals) especially chapter 5 on feature selection.