WebAim, a useful resource website on accessibility issues and topics for the Web, have a useful tool that simulates a screen reader, a device used by the blind to read/access the Web.
The simulation has been made available to better understand what it is like to access the web if you were blind.
WebAim also provide a tool that simulates low-vision for vision impaired users.
Both the tools require the Macromedia Shockwave plug-in.