There are thousands of modules on Drupal.org and too many for us to investigate properly. Here we list some modules that we think would be of use on a large number of website and we have provided you with an installation with most of these modules installed for you to copy (or install) as you like.
An older module allowing you to capture address information easily. Add to the user (people) entity for example to create a membership system.
CAPTCHA checks that a human is using the website and is essential, at least for your user registration form to prevent spamming.
Commerce aims to provide full e-commerce functionality to rival the best of the open source e-commerce platforms out there. Although not quite yet a seriaous contender, Commerce is the right choice for full blown e-commerce with Drupal.
A simple module that allows you to alter the user registration pages slightly so that users can register with their email address instead of a username. You might also look at openid which allows registration with their google or facebook username.
Organic Groups allows you to define groups, perhaps with a user as a manager, and your users can start and join groups as they like. The power of groups is that it allows you to have groups owning content and permissions can be set according to group membership to create shared areas on the website.
Automatically provides a name for the page based, for example, on the page title. You can automatically specify for example that a product entry has the URL http://drupalsite/products/TK1918-Toaster.
Essential for users to search your website. This depends on CRON being run every few hours to index the new content and can be supplemented with the supreme search functonality of SOLR if you have people who can set that up for you.
Taxonomy is used throughout Drupal for organising content and web pages. You can define different vocabularies, perhaps in a hierarchy, for each taxonmomy type or have a free tagging system where the content authors add their own terms for each page. A well implemented taxonomy scheme helps navigation particularly for a large amount of content.
A module that enables display of a 'tag cloud' for a taxonomy type.
Required by PATHAUTO but also lets you specify usernames and other commonly used string inside email messages and throughout Drupal.
SEO helps you abide by best principles for the search engine optimisation of your content.
We have already installed Views - a complex module that lets you define pages and blocks that make lists of nodes. Views is an essential component for creating the navigation pages around your site. It is an eccentric module but extremely powerful.
WYSIWYG is a controversial recommendation and allows formatting when creating content as well as adding images, pasting from word and so on. Some folks like to enable full editing for all content creators whearas others might confine this to super-authors only. An alternave is the BUEEditor which just allows simple HTML formatting.
Remember that Drupal can store HTML in the database but will filter output before displaying on the website. You may find for example you have added an image to the content which does not show on the web page. This is a classic case where you need to change the text filter on that node (or content type).
An easy to configure module for e-commerce particularly suitable if you have a small number of products on your site. There are many additional modules available for tax, shipping, downloadable purchases and so forth and Ubercart is now up and running on Drupal 7.