This module redirects to a user login when a user hits a page they do not have access to.

https

Dramatically speeds up 404 handling. As of this writing, there is a bug when using drush. See this issue for a patch: https://drupal.org/node/2114479 . Thanks to Dan Shumaker for this tip.

Make all external links open in a new window. There are optional custom exclude/include filters.

Lets you use tokens to embed video and have the ability to add a button to the WYSIWYG for easily adding a video (for those to0 lazy to type).

Insert is the easy, secure way to let editors add images and links to files using WYSIWYG editors.

Flag is the ultimate bookmark tool. A must learn module.

"This module defines the "hierarchical_select" form element, which is a greatly enhanced way for letting the user select items in a hierarchy."

The de facto date field for Drupal.