ServerBuddy plugin by PluginBuddy.com tests server configuration to look for problems with hosting configuration and determine compatibility with various WordPress themes and plugins.
Additionally it provides easy to understand explanations of various server settings and generates reports and samples of what to ask your hosting provider if a problem is found with any server configuration that needs fixed.
ServerBuddy is designed to be extremely powerful but still provide information in an easy to understand way for even a novice. Developers of themes and plugins for WordPress may submit definition files for ServerBuddy to allow users to test that a theme or plugin has compatibility with their server.
Plugin homepage: http://pluginbuddy.com/free-wordpress-plugins/serverbuddy/