Mollom

Make spam go away! This is a great service that is free for a low traffic site. A great anti-spam solution for Drupal! Also check out Honeypot and the Bad Behavior module.

User expire

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."

http:BL

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.

env

"This project implements code to make Drupal's configuration (settings.php) environment-dependent, so that you can have different sets of configurations in dev, staging and production. "

Internal Nodes

"Some content/nodes should never be viewed directly; only visible be through something else such as Views or Panels. This module denies access to node/[nid] URLs while allowing the content to stay published and otherwise viewable."

Also see Rabbit Hole

Node Access

The node access module is a popular module and is handy in that you can configure Drupal role based view/edit/create access on a per content type and per node basis.