Nick Lewis posted his list of 40+ Essential Dupal Modules. The majority of the contributed modules on his list should be well known by most Drupal users.
If you are new to drupal, then this list is for you. These are some of the best of the best drupal modules. Everything from standard framework modules, to location and mapping is covered.
Since I've been around Drupal long enough, I don't expect these type of lists to provide me with a whole lot of new information. However, there is still great value in providing these lists for old and new Drupal users alike. For me personally, essential lists provide confirmation for whether or not I'm moving in the direction of more experienced users. Nick's list has inspired me to consider updating in the near-future my own outdated list of essential Drupal modules.