Two powerful tools for communicating requirements from your customers, and testing those requirements, are Fitnesse and Selenium. Fitnesse, a wiki encapsulating the Framework for Integration Tests (aka FIT), enables customers to write sentence-like tests which can be mapped to the underlying system. Selenium drives a browser without all of the fragile mouse coordinate testing you get from a lot of testing tools (ala WinRunner).
FitLibrary provides general-purpose library fixtures (and runners) for Fit and FitNesse. It includes DoFixture, which provides an elegant way of organising storytests in general and of expressing workflow in particular.