There are dozens of great CMSs out there. Regardless of what type of site you’re building, there’s probably one perfectly-suited to it. The problem is that most designers and developers don’t want to spend time learning a bunch of different CMSs. They want to learn one, or maybe two, and use those for all of their sites. That means they need something that’s both flexible and powerful. The CMSs below fit that bill pretty well. Some have practically become household names (in designer households, at least), while others are a bit more obscure.
The first three, WordPress, Joomla!, and Drupal, are pretty unarguably the best CMSs out there. The next seven are a bit more subjective, but have a good combination of support, features, and ease-of-use. Try them out, and decide for yourself which one best fits your needs and the needs of your clients.