Over the years, the networks have prepared a large number of shows for primetime which never actually aired. Sometimes shows will get cancelled early and still have episodes in the can (some of those have now ended up on DVD). Other times series might be cancelled even before their premiere (anyone remember NBC's ads for the 1976 David Brenner comedy "Snip"?)
Besides pilots, I wonder what game show episodes have never actually seen the light of day. Sure, sometimes there were pre-emptions for Watergate and such, but CBS - for one - usually just aired the episode the next day, so there was really very little that didn't get on the air.
Here's what we know of:
"Match Game 79" - the last two weeks of which never aired on CBS
Here's what's rumored:
"$10,000 Pyramid" - the last three weeks of the CBS version before it moved to ABC.
I'm sure there are many others...