is a superb worksheet program. Here you can get some worksheets I created over the years for courses/talks I've delivered and others I made just for geekish fun.
I'm surprised at how people often fail to realize Excel's potential for teaching. With it, a myriad of topics in mathematics, physics, science and, alas, even linguistics can be made visual, interactive and fun. If it were for me, computer spreadsheets would be a mandatory part of high-school curricula.
I encourage teachers to try and use this material in their classes. If you write class activities based on these worksheets, please share! If you like, send it to me and I'll post somewhere here.