Metatag

From the Drupal module page, "The Metatag module allows you to automatically provide structured metadata, aka "meta tags", about a website."

Views

Download over 3.5 million times, this module is an insane query builder. Learn it.

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

Pathauto

"The Pathauto module automatically generates URL/path aliases for various kinds of content (nodes, taxonomy terms, users) without requiring the user to manually specify the path alias. This allows you to have URL aliases like /category/my-node-title instead of /node/123. The aliases are based upon a "pattern" system that uses tokens which the administrator can change."

Token

Gives replacement tokens. This module is used by so many other modules, you are sure to use it and learn it if you haven't already.