Here, I would mention top 3 Drupal Modules without which all Drupal development is waste and which makes Drupal development for most kind of applications a breeze without writing much of code. Writing lesser code also means lesser chances that your code would crash or not work.
The list to useful Drupal modules is almost endless and it is very difficult to find out important drupal modules, but there are 3 giants command on whom is must for every Drupal developer:
This is one drupal module that makes creating forms easy and hence, developers lazy. It does all the validations with a huge set of related cck fields drupal modules like imagefield, email, link, phone etc.
First step in all drupal development is always installation of this module.
Most is good but not all with it. It has performance bottlenecks if your applications becomes complex because of large and unoptimized number of tables it creates. You can still scale with the help of drupal memcache and other drupal performance optimization techniques, but you need more server resources for it.
Again another module that makes you fall for it again and again, once you know its power. It lets you do so many complex things without writing a single mysql query and requiring complex theming. It does so much and so well inside it. You don’t need to write any sql query and it caches those queries in its own cache. Apart from that, you can expose your filters to build nice “advanced searches” around your pages/blocks created on your website.
Last important must-know drupal module for developers is panels. Drupal panels allows us to create different complex layouts of pages. These complex layouts are divided into blocks and each of these blocks can be created with views (and often which in turn are dependent on CCKs).
Get hold of these 3 modules and you would love that you started your Drupal life with them. Thanks to the creator of these modules. They are inventions without doubt.