Seldom seen on Three's Company after about 1980: Suzanne Somers. I believe this was due to her husband's outrageous salary demands for her, back about that time, that the producers of the show either could not, or would not meet, so they limited her time on the show to just a cameo appearance at the very end, in which Jack and/or Janet would talk to Chrissy by phone from wherever she happened to be at the time. And of course, Suzanne was eventually written out of the show entirely.
Also, does anyone remember the '70s House reality show that aired on MTV a few years back? They had a "heard, but never seen" guy, patterned after Charlie on Charlie's Angels, who gave them their marching orders, but whom they never met. On the last episode, they were promised a meeting with him, but actually only got a fleeting shot of him as he left in a limousine!