Fabrik is by far the best forms/tables extension out there. In fact, its a little insulting to put it in with the other 'contact forms' extensions as this is just miles more powerful - its sort of a content management system inside a content management system. you can build nice simple contact forms if thats all the turns you on....or you can build a whole relational database structure with complex forms and a myriad of variables around the tables, groups etc.
Is IS DAFT that its free, but then it really fits with the Joomla idea to have something as well composed as this out there for others to build on.
Lovely vid tutorials (you could write many more, just to show the full scale of Fabrik) are enough to start you off and theres a pretty well supported forum that deals with most of the queries. This should be in its own category of database management software.