This module provides site builders with a way of 'attaching' blocks within the content of any fieldable entity in Drupal. The same block is shown on any entity of that type/bundle.

The Drupal User expire module "allows an administrator to define a date on which to expire a specific user account or to define a period at a role level where inactive accounts will be locked."

"CER keeps reference fields in sync. If you have two entities that refer to each other using Entity Reference (or some other kind of reference field), it saves you the trouble of double-editing your entities in order to have them point at each other. If entity Alice references entity Bob, CER will make Bob reference Alice, and keep the references up-to-date when either entity is updated or deleted."

A must learn module: "This module augments Views by allowing bulk operations to be executed on the displayed rows. It does so by showing a checkbox in front of each row, and adding a select box containing operations that can be applied. Drupal Core or Rules actions can be used."

From the project page, "Implementation of http:BL for Drupal. http:BL can prevent email address harvesters and comment spammers from visiting your site by using a centralized DNS blacklist. It requires a free Project Honey Pot membership. This module provides efficient blacklist lookups and blocks malicious visitors effectively.

A feature packed layout tool that grows on you. Used by many many websites.

Rules is an amazing module with so many features. Among other things it has the ability to send out emails and other kind of notifications based upon all kinds of conditions - just about any kind of notification system can be built with Rules as a foundation. But anyway, just go check it out. Check out the Johan Falk at NodeOne Rules screencasts if you want some good tutorial videos.

Written by John Albin, this module give you more control over the display of menus. It allows you to place the same menu (or different menu) in different regions and customize exactly which levels are shown in each block.

This module uses the FitVids.js library for fluid width video embeds (e.g. flash video in <iframe>s). You don't need it for pure HTML5 videos.
It supports YouTube, Vimeo, Blip.tv and Kickstarter by default, and can use it with other video providers like Dailymotion or Viddler.

This module automatically saves form states using jQuery Sisyphus