Alas, I just saw a notice on the Information Superhighway that he's shaken off his mortal coil and left our plane of existence. Ach, so sad.
A quick look at IMDB.com shows his professional resume was fast approaching an incredible two hundred screen roles, and I believe I've seen him in quite a few of those listed there. (Granted, not all, as I do have a life outside these four walls.) His genre work may not be all that reverential, per se, but there are some great bits in there as well. I'll try to list a few.
He got his first roles in 1979, and that year one of them was as a nameless background character in an episode of the SciFi/Sitcom Mork & Mindy. Then in 1985 he took a (somewhat) big leap forward with some screen time aboard the popular Horror/Comedy Teen Wolf. Some small roles in TV properties like Tales From The Darkside, Max Headroom, and Something Is Out There followed very quickly. Then, in 1991, he found what was probably his first real bit of small screen success playing the mayor of that quaint little tourist spot that went by the name Eerie, Indiana (1991-1992).
Well, I never pass up mentioning appearances in NBC's Quantum Leap, for which he enjoyed a guest spot. Other genre programs include such staples as Strange Luck, The Pretender, Millennium, Star Trek: Deep Space Nine (two appearances in different roles), Early Edition, Star Trek: Voyager, Star Trek: Enterprise, and Medium.
Still, many more roles followed after that, and this guy was indeed prolific.
Also, IMDB.com reports that he had a few roles in projects that are currently in post-production, so who knows what'll happen with some of that stuff? So long as the majority of his scenes were completed, we might have a bit more from this extraordinary player.
Thoughts and prayers are extended to the family and friends of Mr. Itzin.