Drupal is a great Content Management System out-of-the-box, but one of its real strengths lies in its extensive variety of modules. There are a number of modules which are so useful that we generally always install them with every Drupal implementation that we do.  I've listed them here grouped by general function for you.

Usability

One of Drupal's biggest criticisms is that it is not inherently as user-friendly for non-technical users as compared to alternative CMS solutions, such as Joomla [1] or DotNetNuke [2].  The following modules help to address this concern:

• Drupal Administration Menu [3] - Drupal's text-based administrative menu system can sometime be daunting for novice users coming from another CMS.  The Drupal Administration Menu provides a theme-independent administration interface that provides for quick and easy access to all administrative components in the form of a drop-down navigation menu that hovers over your site at the top of your browser. It's a real helper for non-technical users, a real time-saver for Drupal site administrators, and definitely a must for Drupal developers and site builders.
• FCKEditor [4] - Every Content Management System needs a WYSIWYG editor for non-technical users.  Drupal supports two editors that must be installed as modules, this one and the TinyMCE [5] editor.  We have found the FCKEditor to be easier to install, easier to customize, faster to load in your browser, and generally more stable.
• IMCE [6] - A WYSIWYG editor is not nearly as useful as it might be if it doesn't provide a simple way for a user to upload images or other files from their desktop.  IMCE is used in conjunction with FCKEditor and other modules to give users these capabilities.

Search Engine Optimization

Most websites are concerned with search engine optimization and high rankings on search engines. Drupal features a number of modules that readily work to improve rankings:

• PathAuto [7] - This module automatically creates user-friendly URL aliases based on the node title, without requiring you to manually set it up.  One tip: change the seperators to - or + because Google takes _ as hard separators, while it takes - or + as concatenation.
• Meta Tags (a.k.a NodeWords) [8] - Allows you to specify meta tags (specifically keywords and description) for a node.
• Page Title [9] - Allows you to specify the HTML Title for a page.
• XML Sitemap [10] - The XML Sitemap module (formerly the Google Sitemap Module) creates a sitemap for you in accordance to the sitemap.org [11] specifications, which is supported by Google, Yahoo!, Ask, and other search engines.

Website Statistics

• Google Analytics [12] - The built-in reporting that Drupal offers is relatively limited, and Google Analytics has quickly become one of the most widely used website statistical packages.  This module allows you to easily implement the freely available stats package in your Drupal site, all you need to do is setup an account [13].

Content Related

• Views [14] - The Views module provides a flexible method for Drupal site designers to control how lists of content (nodes) are presented. Traditionally, Drupal has hard-coded most of this, particularly in how taxonomy and tracker lists are formatted.
• Content Construction Kit (CCK) [15] - The Content Construction Kit allows you create and customize fields using a web browser.

Preventing SPAM-Bots

• CAPTCHA [16] - Definitely install this module if the site is going to have forms of any sort, even contact forms. Eliminates forms being submitted by SPAM-bots by requiring the user to input a response to indicate that they are human.