Probably one of the best ways to add meaninful content that changes and refreshes regularly would be to add a blog to your site. Regular blog entries (they don't have to be long, often a paragraph works) bring the search engines to your site as often as a new post is made and blogs often rank higher than a regular website.

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Yak long and prosper, Bonnie Dillabough
Chief Imagineer, www.Yaktivate.com