TextPattern
From ToolCenter
TextPattern is an open-source content management system by Dean Allen with a very clean interface that relies on PHP and a mySQL backend. Images are kept in a separate gallery, from which links to include in posts can be generated.
TextPattern also includes integrated Textile support,for those who want to use the "humane web text generator." However, TextPattern requires substantial knowledge of CSS, and dosn't have the default templates of other CMS systems like Movable Type.