Dynamic Content Type? (field appears based on previous taxonomy choice)
Try out the Conditional Fields module.

Conditional Fields for Drupal 7 is an user interface to the new States API, plus the ability to modify fields appearance and behavior on certain conditions when viewing content.
Conditional Fields allows you to manage sets of dependencies between fields. When a field is “dependent”, it will only be available for editing and displayed if the state of the “dependee” field matches the right condition.