I’ve been using the Moodle database activity. It’s a great tool and highly flexible.
One of the ways I have used it, is for creating shared learning logs. All students on a course log each time they put something they have learned into practice. You could just use a blog for this, but with the database you can specify the kind of information that you want to capture. Students can see one another’s logs and you can also allow them to comment or rate the logs.
I’ve also used it to create lists of resources – e.g. useful blogs for e-learning developers. You can see a demonstration of how I did this here.
The only downside is that, by default, when you view entries in the database, it is a bit of a mess. You need to know a bit of HTML to really get the information to display the way you want it to.