If you have come across a site that is inaccessible, and you want to let them know of the importance of accessibility for a web site, and ask them to make efforts to make their site accessible to all, it is a good idea to send the webmaster of the site a message expressing this. Although many sites ignore such letters, there are also many that are receptive to visitor complaints and they may make their site accessible if they receive enough requests.
In fact, many sites claim that they don't make their pages more accessible because they don't think their visitors need them to be, and quote lack of complaints as their reason. Make sure that sites you visit know it's important to be accessible by everyone. Don't let ignorance be their excuse. You may want to encourage them to visit the Accessible Design Guide at: http://www.anybrowser.org/campaign/abdesign.html for advice on how to make their sites more accessible.
Below are some example letters that have been sent by participants in the campaign, that you can modify for your own use when you notify sites that they're inaccessible and that you want them to fix it. If you have any example letters that you think should be listed here, please let me know.
Polite commentary requesting the site make their pages usable by any browser
-Courtesy of Peter Froehlich
Polite and to-the-point request for alt text on graphics-only page
-Courtesy of Ramon Casha
Polite request for alternative text on a site accessible only with graphics
-Courtesy of Bryony Lake
Polite Request to send to a Java/Frames site that is inaccessible
-Courtesy of Jean Yim
Another polite Request to send to a Java/Frames site that is inaccessible
-Courtesy of Robert T. Butler