Although there are many different types of disabilities out there, it is possible to create a site that will be accessible to almost all of these people. Some of the more common disabilities are below:
Blindness
Pretty obvious that those who are blind will not be able to see a fancy graphics and pixel-perfect layout. They visit your web site for the information, not the presentation, and making a site accessible to them will need to focus on properly coding your HTML. To aid in this approach, think about HTML Semantics! What does the code mean. Also think about validation - make sure the code is correct.
These people primarily browse the web using screen readers and other devices that will try to read the content of the site and translate it into either voice output or Braile. Using Semantic HTML will allow these people to access information on your site. You should also consider those who are partially blind (i.e. poor visual perception). These people will have difficulty reading the 8point fonts used in many web sites today.
Color Blindness and Partial Blindness
Color blindness is actually fairly common. Although there is some debate about the actual number, about 1 in 10 people have some type of color blindness. The most common type is red-green color blindness, which impares the ability to distinguish between red and green. The second most common, but far more rare form, is yellow-blue color blindness. The most common assumption of color blindness, is a form that people usually think as the most common, but is actually quite rare. That is complete color blindness, or the inability to identify any colors.
Physical Disabilities
There are various other physical disabilities that can restrict a person's ability to use a web site. These may include Parkinsons, ALS, arthritis, and many other neural and muscular degenerative diseases. Often these disabilities will restrict a user's ability to use a keyboard or operate a mouse, which means that you will need to provide alternative methods for browsing your site.
But what do I do?
Run your site through a thourough evaluation of the W3C WAI guidelines and check list. Here's our evaluation on the UDM4 menu:
http://www.udm4.com/menu/accessibility/
And here are the item from W3.org
http://www.w3.org/TR/WAI-WEBCONTENT/
Till next time...