Devel

Essential module for developers. Should be disabled in production environments.

Security Kit

"Module provides Drupal installation with various security hardening options. This lets your mitigate the risks of exploitation of different web application vulnerabilities."

Search Krumo

Use search Krumo Search to extend Devel to get a search box for your dpm(). A new search box appears above all krumo prints.

If you use sdpm(), you get a really nice feature that lets you copy the full path of the variable, "for the lazy programmers"...

Bundle copy

Bundle Copy is in Drupal 8 Core CMI. It is a replacement for the Content copy module which lives in the CCK project for Drupal 6.