Letter spacing. Read this.
Two European researchers have demonstrated that increasing the spacing between letters help students with dyslexia read faster, bumping up their reading ability by about a year. Their app for testing your best reading spacing, DYS, is free.
Robert Lee Hotz has the details.
Unlike having to use expensive fonts, like dyslexie, letter spacing is very easy to change on a webpage, and anyone should be able to change the preferences on their browser; for Mozilla Firefox you can change the letter-spacing using User CSS (which is not quite as easy as changing it in the preferences).