Wow, I get to be the first to mention St. Elsewhere! 
I have every episode on tape (and commercial-free, thanks to PBS), and every couple of years I’ll spend a few months watching them all. I’m currently at the start of the 3rd season, for something like the 6th time.
I’ve also seen every episode of:[ul][li]All Creatures Great and Small (thanks for the reminder, eleanorigby!)[/li][li]Firefly[/li][li]Lost[/li][li]Alias[/li][li]Eyes[/li][li]Friends[/li][li]Seinfeld[/li][li]Wings[/li][li]The Office (UK)[/li][li]The 4400[/li][li]The Pretender (and both movies)[/li][li]Nip/Tuck[/li][li]Desperate Housewives[/ul][/li]
I think I’ve seen every episode, but can’t swear to it, of:[ul][li]Buffy The Vampire Slayer[/li][li]Angel[/li][li]Farscape[/li][li]Stargate SG-1[/li][li]The West Wing[/li][li]Monk[/li][li]MASH*[/li][li]Sex and The City[/li][li]Roseanne[/li][li]Fresh Prince of Bel-Air[/li][li]Cheers[/li][li]The Drew Carey Show[/li][li]Friends[/li][li]Frasier[/ul][/li]
And via Netflix, I’m working on seeing every episode of:[ul][li]The X-Files (I just finished Season 6; I saw seasons 7-9 when they aired, but missed a show here and there)[/li][li]To Serve Them All My Days (another old British show)[/li][li]Carnivale (finished Season 1)[/li][li]Entourage (finished Season 1)[/li][*]Family Business (finished Seasons 1 & 2)[/ul]I don’t have any pay cable channels, so I’m usually a season behind shows on HBO or Showtime. Someday I plan to get all caught up with The Sopranos and Queer As Folk, too. 