I find that the major advantage to using a CMS is that you don't have to babysit your site for the rest of it's life. You can literally set it up, hand over the keys and your customer can take care of the details if they need changes at a later date.
They are also ideal if you're aiming for some UGC (User Generated Content) as you can set up many users to help with the content.
I personally love
phpwebsite and use it in most of my projects for clients.
It's Open Source and easy to figure out plus has a large community to support it. It's driven by PHP and MySQL and is a lot more customizable in terms of layout and functions then the others I've worked with in the past.