Here is a list of free drupal modules that will make your work easier during development and site administration.
Devel module provides helper functions for drupal developers.
This module provides a theme-independent administration interface. Its a time-saver for site administrators, and useful for developers and site builders.
No matter which content management system you are using, an important thing is to have easy and quick way to backup or restore the site. Backup and Migrate module allows you to back up and restore your Drupal MySQL database, code, and files or migrate a site between environments.
Display Suite allows you to take full control over how your content is displayed using a drag and drop interface.
Views is an excellent module with over 900,00 installs and still counting. It has also been included as a part of drupal 8 core. Primary purpose of views module is to display content in a nice/custom format that can be configured easily via views UI.
This module aims to accomplish the ability to quickly find the module you are looking for without having to rely on the browsers search feature which more times than not shows you the module name in the 'Required by' or 'Depends on' sections of the various modules or even some other location on the page like a menu item.
DraggableViews makes rows of a view draggable i.e. they can be rearranged by Drag 'n' Drop.
Administration module replaces administrative overview/listing pages with actual views for superior usability.
The features module enables the capture and management of features in Drupal. A feature is a collection of Drupal entities which taken together satisfy a certain use-case.