When describing my services, I try to avoid talking too much about the underlying technology. To most customers these decisions do not (and should not) matter. What does matter are the features, stability and scalability of the final product. To achieve those things, a developers' talent matters as much as the technology used. Still, some customers are savvy and/or curious enough to ask, so here's a description of my preferred development environment.

• Drupal Labelled a CMS, framework or plumbing. Call it what you like, its an wonderful platform for developing web applications. Many sites use it and there's a thriving community - this means bugs and security holes are likely to be discovered and fixed. The built-in features are vital to most sites, and almost-too-many contributed modules enable it to do much more. As a developer, hooks allow me to customize any aspect of the sites behavior. And that is critical in making customers happy.
  I am an active member of the Drupal developer community.
• PHP a popular scripting language, specialized for developing websites. I try to remain language-agnostic, recognizing that all software has both strengths and weaknesses. PHP is my preferred choice because it is very widely used, and the majority of web hosting services support it. Also it is the language of Drupal.
• MySQL Again, widespread adoption and the support of many hosting services make this my choice. Not necessarily because of any technical superiority over postgres or other databases.
• Subversion An excellent source code control system. Keeps revisions of all the software I write. This helps in tracking down and fixing bugs. It's vital when collaborating with other developers.
• Apache A proven, reliable, and widely supported web server.
• Unix Most hosting services offer some flavor of Unix. My preferred hosts rely on Linux or BSD.