JAWS, a screen reader and navigator for Windows. A time-limited, downloadable demo is available.
Lynx, a free text-only web browser for blind users with refreshable Braille displays.
Links, a free text-only web browser for visual users with low bandwidth.
Opera, a visual browser with many accessibility-related features, including text zooming, user stylesheets, image toggle. A free downloadable version is available. Compatible with Windows, Macintosh, Linux, and several other operating systems.