In 1986, at the height of his career (as It's Garry Shandling's Show was starting), comedian Garry Shandling did a Pizza Hut ad. Here it is:
It appears to be part of a major campaign, also featuring standup comedian Roseanne Barr (whose show Roseanne didn't start until 1988), actor Pat Morita (whose turn in The Karate Kid was in 1984 -- I suspect this video is from 1986 despite the YouTube description), and actress Rita Moreno.
If celebrity endorsements aren't your thing, here's a strangely touching commercial for the Pan Pizza and a strangely ethnically insensitive commercial for the Calizza, a sort of proto-P'Zone. Oh, and don't forget that you used to be able to get free Crystal Pepsi with your Pizza Hut pizza!
Don't even get me started on Book-It. That's a whole different blog topic.
(Shandling commercial via @jmerriman.)