What's that website where you can look up past shows on American TV?

I’ve seen a website where you can find a listing of just about everything that was ever on (network?) television in the U.S.: old TV series with their start and end dates and all the episodes, and specials such as Hallmark Hall of Fame going way back, with dates and synopses and principal actors and so on.

I’ve looked things up there before, but I lost my bookmark and can’t find the site now. Do you know what I’m talking about?