Updated 5/8/06
The CCK (content construction kit) module was released only 2 days ago. I've been working with it for only the past 2 hours, and I'm ecstatic. In terms of its overall usefulness, I'd say its in the same category as simplenews, views, and tinyMCE (read: no drupal developer, consultant, or amature should be without it).
In many ways, this module will likely signal death for flexinode. Which doesn't really bother me, because I never used flexinode. While flexinode still has more 'flexibility' in terms of defining all varieties of different fields, it has serious themability issues which have prevented me from ever using it. Moreover, where as flexinode created something of a pseudo-node type, CCK creates full fledged node types that have all the options, workflows, and permissions levels. But perhaps most exciting is how easy it is to theme your custom fields. To get you started, I've written a quick tutorial on exactly that:
