Devel is a supremely useful module for Drupal development, but if you've never enabled the Development menu block, there are some useful links you might be missing out on. Here are some features of Devel that you might not know about:
Execute PHP
Path: devel/php
Provides a text area for entering PHP code into. Any output (print, print_r, var_dump) is shown in a drupal_set_message.
PHP Info
Path: devel/phpinfo
Get PHP configuration info from the server your site is running on.
View Theme Registry
Path: devel/theme/registry
Get down deep with the theme info your Drupal site knows about. Great for expert themers.
