Top 10 drupal modules you must have
There are several modules I have used during building sites. I am not going to get into details of the modules because you should visit the modules. But by far, the most important / useful modules for me have been:
1. Views ; You can think of views as output to your custom query (except you don't write the query). There are several ways to present the views and Calendar is one example. So this is a query builder which can execute queries at run time and present the data however you want.
2. Content Construction Kit ( CCK ) : You can add custom fields to a node or define a new content type based on CCK, This is powerful functionality with no coding. You can order the fields according to your preference. And CCK will become very powerful once Multigroup is introduced. As of now, Multigroup is in alpha, but I have been using it with no problems. It lets you create a composite or a compound field, consisting of different base CCK fields.
3. Admin menu : The module renders all administrative menu items below 'administer' in a clean, attractive and purely CSS-based menu at the top of your website. This is a life saver if you are administering a site. Essentially it is a overlay of the entire admin functionality as a ribbon on the top of your web site.
4. Sheetnode : I have to give it to katrib for this module. This is great if you want spreadsheet functionality in your website. We did some pretty advanced things with the module like embedding it within a node as a tab and YUI integration. We also configured a java bridge to be able to upload excel sheets from desktop to the website. Google spread sheet integration is pretty straightforward. This is based on SocialText platform
5. Organic groups (og) : Enables users to create and manage their own groups (like forums). This can bring great social aspects to your website. For some of the sites, we changed the module to represent a company and it was great.
6. Dynamic display block (ddblock) : This adds a lot of umph to the site. It is Mainly used to showcase featured content at a prominent place on the frontpage of the site. Demos and tutorials are excellent.
7. Devel : Essential for developers and themers It can generate SQL query summaries, create data for your test site, show the theme information on your site. Don't develop without this module.
8. Pathauto : It automatically generates path aliases for various kinds of content (nodes, categories, users) without requiring the user to manually specify the path alias. Helps get rid of default / ugly paths (node/3 ... )
9. jQuery : jQuery depends on jQuery UI and jQuery update in drupal 6. And here is a good overview of jQuery.This architectural diagram might also be a useful reference. jQuery modules provides all the nice functionality jQuery library.
10. Logintoboggan : This module provides several useful extensions to the login system of drupal. What I found really useful was to allow email based logins, email confirmation during registration and auto logout. Happy drupaling :)