With the addition of custom fields in the core Joomla! installation, smaller CCK projects can be accomplished without additional extensions. Some sites require more options than these new features can offer.
We have worked on several projects that use Flexicontent CCK. This component uses the core content within Joomla! and so it works with most every other plugin that works with Joomla and can be easily adapted to most situations. We also have experience with many other content creation components including SOBI, K2, Zoo, and Content Builder.