If you need a simple great looking site with mostly static content, up to 30 pages, and no need for custom complex forms, or ecommerce, GetSimple is a great choice. If you already have an investment in a static HTML site, and would like to keep the same design, but enable easy browser-based access to content editing, it is easy to convert your current site to a GetSimple content-managed site.
Budget: starting at $500.
WordPress is the standard for blogging sites, and can also work very well for static content sites. WordPress benefits from an easy to use admin panel with many easily installable templates and plugins. There are also plenty of beautifully designed pro templates for WordPress.
Budget: starting at $1,000 (depending on plugins, theme, customization etc..)
Joomla is the premier mid-level CMS, and is generally the best for most companies who need a lot of functionality, room to grow, and easy updating. Joomla is extendible, and there are literally thousands of components that can offer virtually any functionality needed. In addition there are innumerable templates in almost every possible style.
Budget: starting at $1,500 (depending on plugins, template, customization, ecommerce, CCK etc...)