I've been hunting around for a listing of all the available debian
metapackages but can't find one. Can someone please point me in
the right direction?

yields a small number of results, but it doesn't look complete.

Unfortunately, although the debian package listing page (ex.
for stable http://packages.debian.org/stable/ ) has a "Virtual packages"
section (which I realize is very different), I don't see a "Metapackages"
section -- which would be very nice.

Just out of curiosity, what would you want this for? I can't see much of a use for it, so I don't imagine there is an easy way of getting it.

Whoops. Sorry for the late reply.

Suppose I want to install some large piece of software -- one that, I'm guessing consists
of multiple packages (I'm thinking of Gnome at the moment, but I figure there's others
like it). It stands to reason that there may be related packages that would be helpful, but
that I may not realize I could stand to have around.

Primarily, I'm thinking of Gnome, since:
1. it's got such a sprawling number of packages associated with it,
2. I don't see a metapackage listed for it at http://packages.debian.org/stable/x11/ , and
3. I wouldn't know which ones I needed if I wanted a somewhat complete "Gnome" installation.

Hmm... I guess I've answered my own question: in most circumstances, I could just
hunt around (apt-cache search) and look at various package's "Recommended" and
"Suggested" listings, and then put together my own little list of what I want to install.

Gnome may be an exception because of it's size and large number possibly-useful
packages that I don't have experience with.

apt-cache search gnome is the right way to go about it. You can refine it more by doing greps on that or adding keywords like "desktop environment", because just searching for gnome returns a lot. In general, you might try and see if there's a package with the exact name you think there is (like, gnome) and then examine that to see if it's what you want.

You don't see it in the x11 section because there's a whole gnome section

By the way, I recommend doing all of this (except the apt-cache search, but definitely for looking at packages and installing them) in aptitude

Thanks Strike.

Never tried aptitude. apt-get and apt-cache seem pretty straightforward to use.
I'll have to give aptitude a try.

I earnestly tried learning to use dselect once, but I never was able to make heads
or tails of it with the docs available.

You don't see it in the x11 section because ...

Ahh. You must be referring to using aptitude here, since I don't see anything about
"sections" with apt-get. :)