The Helen Project is an initiative by the American Foundation the Blind to provide all internet users, especially people with disabilities, the opportunity to register publically available feedback on the accessibility of sites they use:
We offer you a free downloadable, fully accessible, web site rating toolbar application (which we affectionately named “Helen“) that will enable you to have your voice heardas you experience problems and/or success in using any web site. And, most importantly, Helen will enable the collective voice of the user community to be heard by web site providers,
To be part of the Helen project you need to register. Users can then participate by installing a free browser toolbar to rate web sites on web accessibility. Currently the toolbar is only compatible with Internet Explorer for Windows versions 5, 6, and 7.