A friend has asked me to recommend a resource so that he can learn more about
using Excel effectively. He is using Excel 2007, but I think that Excel 2003
resources would work as well. He can manage basic formulas, but is aware
that the potential is essentially infinite ... I have crawled around the web
and found many tutorials, but don't really know what to recommend to him.

Has anyone here used Excel tutorials? Could you recommend something?

Thanks so much!