Readability Test

This is about content readability which finds its way in the Web Content Accessibility Guidelines. Douglas Karr mentions the readability test at Juicy Studios. This readability test is based on the Flesch and Flesch-Kincaid Methods and the Gunning Fog Test. These algorithms can be useful for readability analysis and can help you in taking steps to make it easier for your readers. The test page also has information on how to interpret the results.

UPDATE: Amit has one more tool.

If you are a Wordpress loyal, you can use Word Statistics plugin, that had introduced me to this analysis. Having said this, the result can often get influenced by the topic and the audience that you write for. For example, you you might end up using a lot of jargon if you write a technology blog, which can go against you. However, some results like, average words per sentence can be used to improve readability.