Well, you've probably all had a White Screen Of Death a time or two while dealing with Drupal or PHP. They can be very frustrating, but are usually easy enough to resolve. The following illustrates how to recover from a Drupal WSOD as a result of making changes to your cache settings in the Site Configuration -> Performance admin page. Again, this "fix" should only be applied if you have issues that you know are related to recently altering the cache/aggregation/compression settings.
FirePHP is a great tool for debugging PHP, and maintaining some level of control over your error handling. Also, it's a great tool for getting information about your variables, objects, etc. while your PHP code is executing. FirePHP requires only a small amount of setup and can be reused time and time again without tedious setups for each site on your server. This tutorial/example requires Firefox.