What's the simplest way to make a HTTP GET request in Perl?

LWP::Simple:

use LWP::Simple;
$contents = get("http://YOUR_URL_HERE");

LWP::Simple has the function you're looking for.

use LWP::Simple;
$content = get($url);
die "Can't GET $url" if (! defined $content);

Take a look at LWP::Simple. For more involved queries, there's even a book about it.