Juicy Studio: Readability Test
Writting is still a form of art. Gunning Fog, Flesch Reading Ease, and Flesch-Kincaid are reading level algorithms that can be helpful in determining how readable your content is.
Reading level algorithms only provide a rough guide, as they tend to reward short sentences made up of short words. Whilst they're rough guides, they can give a useful indication as to whether you've pitched your content at the right level for your intended audience.
Quote from John Dowell (Macromedia): I found this while running the search engines... enter an URL, and it calculates sentence length, syllable distribution, vagueness/clarity, gradeschool level. Seems like this could be a useful tool when presented with weird copy by a client...?