<p>I guess the question is self-explanatory, but I'm wondering whether HTML qualifies as a programming language (obviously the "L" stands for language).  </p>

<p>The reason for asking is more pragmatic&mdash;I'm putting together a resume and don't want to look like a fool for listing things like HTML and XML under languages, but can't figure out how to classify them.</p>

YES, a declarative programming language.
You really want to list the most important things you know that are relative to the job you're applying for on your resume. If you list ASP.NET but don't list HTML, even though it's somewhat obvious, there are a lot of managers and/or HR types that will assume you don't know HTML since it's not listed. I've had it happen to me before.
Update - Some say no it isn't a programming language, and you may not agree with me on this, but regardless on a resume it IS a programming language. You get HR types looking at your resume before the hiring manager even sees it. If the manager says you need to know HTML, and it's not listed in the 'programming languages' section then the HR person may disregard you resume thinking you don't know it because it's not listed.
Update 6-8-2012: Any instruction that tells the computer to do something is a programming language. So even after all these years, I still stand by my answer. HTML is a programming language. Something that isn't a programming language would be XML.