Content Management Systems
Have tried them all, many of them are very complicated but there are a few simple, useful ones too.
The complicated ones allow web based administration of much of the "presentation" or "look" of the web site and add extra layers of complexity; for example moving blocks of content around. The ability to assign "permission" levels and hide/show pages based on a user and/or time frame, extra modules and admistrative layers is also often found with varying degrees of admistrative complexity.
Website Baker & Wordpress
Each uses the existing CSS and xHTML that already displays your web site as the basis for their internal templates, and basic conversion including approx. 6 to 12 pages of content is $149. It is probably a good idea at the same time to get the HML markup to modern standards as well if not already done.
Often a client will want to have some form of content control for their web site and most of them are not inclined to learn any HTML. Both Word Press and Website Baker are popular solutions for this and their template systems allow them to be applied to any design. With Website Baker, multiple content areas on the same page can be implemented for finer content control.
Although the presentation (the look of) a web site can be duplicated with either program, Wordpress is better known than Website Baker. Both have easy to use administrator interfaces, with Website Baker having the most options for customization and the ability to install a wide range of differnt wysiwyg editors for editing site content.
Which one to use? WP has limited editing abilities, in some cases you don't want your client to be able to easily change much either in the admin or the content shown and that's okay. If you want a more advanced but not complex (like say, Drupal) system, Website Baker takes the least amount of end user training compared to more complex software.
Demo installations of both are available:
http://start.websitebaker.org/en/demo.html
http://www.opensourcecms.com/index.php?option=com_content&task=view&id=2143