I have been using Drupal as a beginner for a while now, and have come to find that I was doing everything the hard way (editing code directly to make modifications). Recently, I went to a great Drupal conference in Philadelphia (Drupaldelphia) where I learned a lot about ways to streamline the process and make Drupal easier and accessible to more people. Drupal is a great content management system that is very flexible and customizable for any type of client, especially for larger sites that have a lot of content. The best part is that it is free and open-source, with help available via their user forums. 
Read more about some very useful Drupal modules below the jump
- Feeds – http://drupal.org/project/feeds (D7 beta)
Import or aggregate data as nodes, users, taxonomy terms or simple database records. - Dashboard – http://drupal.org/project/dashboard (D6)
can create custom views for each user role
creates a homepage overview of the site that is easy to understand for non-techy folks - Workbench – http://drupal.org/project/workbench (D7 only)
integration with media files
draft view/unpublished items
integration with workflow and access views via user role - Reference Preview – http://drupal.org/project/reference_preview (D6)
when adding a node reference, it allows you to see a preview of the content (teaser + image) - Block Reference – http://drupal.org/project/blockreference (D6 & D7)
same as above, but with blocks. Example: reference the sidebar content for a member discount after user has logged into the site. - Node relationships – http://drupal.org/project/noderelationships (D6)
allows you to create children of other nodes - Login destination – http://drupal.org/project/login_destination (D6 & D7)
Route people to a specific page after login, to the dashboard perhaps, can be edited based on user role. - Markup – http://drupal.org/project/markup (D6)
create contextual help within the node creation form - Node form settings – http://drupal.org/project/settings (D6 – I think this is the right link)
remove any unnecessary things that may confuse or deter non-techy users. - Multistep – http://drupal.org/project/multistep (D6, D7 beta)
splits a giant form into more manageable steps - Conditional Fields – http://drupal.org/project/conditional_fields (D6, D7 beta)
enable/disable form fields based on contextual need - Views Bulk Operations – http://drupal.org/project/views_bulk_operations (D6 & D7)
able to do bulk actions, based on conditions checked - Edit View – http://drupal.org/project/editview (D6 only)
view node edit forms stacked on top of each other, so all can be completed at once - Editable Fields – http://drupal.org/project/editablefields (D6)
gives people the ability to edit fields right on the page without going into node edit (works with CCK). Might be a good idea for simple things that a content user could edit a single item but still not give them admin editing access. - WYSIWYG – http://drupal.org/project/wysiwyg (D6 & D7)
allows a force cleanup on paste, you can set up different abilities based on user role. Works with CCK.
** remember when using this & CCK – only use specific styles from your CSS file available in your dropdown menu… or eliminate the style dropdown completely to help keep content look consistent. - Media – http://drupal.org/project/media (D7 beta)
good image/file management tool if this type of thing is needed for your site. - Browscap – http://drupal.org/project/browscap (D6)
a module to determine what browser a user is using (for mobile sites or for analytics) - Wurfl – http://drupal.org/project/wurfl (D6)
helps detect devices - Mobile Tools – http://drupal.org/project/mobile_tools (D6, D7 beta)
a module that assists in making a site mobile-friendly. Detection of user agent, redirect to mobile site, automatic theme switching, integration with Panels and many other features - Panels – http://drupal.org/project/panels (D6 & D7)
The Panels module allows a site administrator to create customized layouts for multiple uses. - CTools – http://drupal.org/project/ctools (D6 & D7)
required to work with Panels - Features – http://drupal.org/project/features (D6 & D7)
this module allows you to capture and export your code into a features module – this is good to do when using panels and you have overly complex code. This can be used as a backup of the code. Easier to recover your panels configurations if they are changed or modified. Recommend “syncing” daily if on a heavy traffic website. - Arrange Fields – http://drupal.org/project/arrange_fields
arrange node input fields or web forms with a simple drag & drop interface - Mega Menus – http://drupal.org/project/megamenu
allows for fancy dropdown menu features such as icons, images, two-column dropdowns - Views Slideshow – http://drupal.org/project/views_slideshow
jQuery slideshow that can create a slideshow of any content, not just images. - Quicktabs – http://drupal.org/project/quicktabs
allows you to create blocks of tabbed content - Webform Alt UI – http://drupal.org/project/webform_alt_ui
requires other modules to work, but allows drag & drop building of web forms. More of a web forms for dummies ☺ - elFinder – http://drupal.org/project/elfinder
open source AJAX file manager - Chosen – http://drupal.org/project/chosen
jQuery plugin to allow you to select multiple items from a drop-down menu
**note at the time this post was written, Drupal is in transition between Drupal 6 and Drupal 7. Drupal 7 core release is available and stable, however many of the modules have not yet been updated to work with Drupal 7, so a lot of people are still using Drupal 6. This will likely change as modules are updated and Drupal 7 becomes more widely accepted.