I'm a developer for an organization that is starting to plan out how to overhaul a number of our web applications with a focus on making them both 508 compliant, and truly accessible for users with a variety of disabilities. We're a small company and relatively small development team, and at this point, none of us really know how to test that we've made something accessible, other than following some of the standard checklist items that are part of the 508 spec.
If we want to move beyond this kind of simple box-ticking and really test that we're making something accessible, where should we start? What sort of tools or applications (i.e. screen readers, etc) should we invest in? What additional staff or client testers to we need to include in our process?