Drupal requires a few modules before it can be truly functioning to one's expectation. The three sites listed below are more than enough for the beginner. As it is, some of the modules are only relevant if the website to be built is of a particular type - community, commercial, blog, etc. That said, the one module that must be installed would be the WYSIWYG editor. The default Drupal content creation way is to type in the page wholesale with all the markup which is a pain!
Top 10 Drupal modules
10 Drupal Modules You Can't Live Without
Drupal Podcast No. 40: Top 40 Projects
TinyMCE WYSIWYG Editor
widgEditor - A WYSIWYG editor