Features, features, features!
There’s a brand new page on EllisLab.com that covers all of the features in ExpressionEngine.
It’s broken up into categories and then you just click on the feature to get a short blurb that describes what that feature does.
This is a great page to point people to when they want to get more detail on what ExpressionEngine does. Or maybe to help you reinforce your recommendation of EE as the CMS solution for a project.
Bookmark it and refer people to it.