Tools for blind & partially sighted users?

Does anybody know of any tools, plugins, themes, etc which have been designed with blind/partially sighted users in mind?

I’ve been asked to create a website for a blind charity, and I’m looking for ways to make things easier for users.

The site is for both blind/partially sighted and normal users, and I’d prefer free items as I’m doing this free and would prefer not to have the charity pay out for anything, enabling their money to go to more important things.