Wordpress, Joomla, Mambo, Drupal... All are open source and great options. Each have their ups and down. One of the downsides of them all are the learning curve.
Wordpress is good for blogging but harder to learn how to customize an entire site around. (I cannot say much for wordpress as I only use wordpress in association with Joomla and Corephp)
Joomla I personally swear by for building sites with as from an optimization point of view every page can be given meta tags and keywords without coding or database experience. It has tons of free tutorials, free templates and free modules to make it do anything you want. Some have complained of security issues with the login page (although you won't likely need front-end login options). In 4 years I have never had a security breach and you can always encrypt the login (which is something I have done now for all clients) and then you have zero risks even with front end login.
Drupal is said to have more security then Joomla but has less flexibility and modules.
Mambo is simular to Joomla but a bit behind in technology and outdated in many ways.
Again I do prefer Joomla so my post may be a bit biased but without programming experience an open source, free, content management system is, in my personal opinion, your best option so that you are not paying out a fortune for webdesign,
SEO, and updates.