I'm going to throw my vote in for Gtkperl as well. You can find a very nice tutorial for it here.

I'm also going to vote against using HTML/web-browsers. I love HTML, but I think there is a limit to stretching a technology into an area that it wasn't designed to handle. If you want to send a few sets of large data, HTML is great. If you are sending many packets of small data (such as when you want an instant response to, oh, say, a volume change), HTML is horrible.

Of course, the best way to do it is to write your code into a module/API, and call it from a wrapper script. Thus you might make Gtkperl your first interface, but it only takes a few lines in a CGI script to run it from HTML, and if the next guy to come along decides that he likes your functionality, but hates the interface, he can rewrite it in Perl-Tk without starting over from scratch.