This has all been interesting, but ...
... if you read the original poster's request, he wants something that would allow a search across the schedule of every network and television station, nationwide.
I have kept out of this because I don't know of any such site, but I don't believe the answers that have been posted are particularly helpful, given what he is looking for.
My guess as to why such a thing does not exist is that (1) 99.9% of people don't need/want such a search engine, being only interested in what is available on their own television set; and (2) imagine what a search on something like "That 70's Show" would look like, as it would turn up the first-run episodes on every Fox affiliate, the repeats on F/X, and the repeats on every station that ran them ... that likelihood would probably scare off any listings provider in terms of designing something where a search didn't overtax their database.<P ID="signature">______________
</P>