TV series you've seen every episode of..

MASH
Twilight Zone (as many as can be seen in reruns, anyway)
Night Court
WKRP in Cincinnati
Head of the Class
Lou Grant
The Prisoner

There are probably more, but those are the ones that come immediately to mind.

As far as the Twilight Zone questions go, you might want to refer to the Twilight Zone Companion, by Marc Scott Zicree. It explains a lot about the “Owl Creek Bridge” story, as well as the episodes that were not released in early syndication packages (for example, “Miniature”). I don’t have my copy with me right now to settle the questions, but it could probably be found easily enough.

The Andy Griffith Show (but not once Andy left)
Magnum PI
Seinfeld
The Adventures of Pete & Pete
The Simpsons
The State (See my sig)
Moonlighting
The Adventures of Brisco County Jr.
I’m betting that there’re more, but I can’t think of them right now.

Does it count if I’ve seen every episode, but not by choice?

Cuz I think I’ve seen every single episode of Arthur, Dragon Tales, and Zoboomafoo ever made. Like 3 times each.

Every episode?

Babylon 5
Moonlighting
Twin Peaks
Seinfeld
, probably
Wiseguy - I can’t believe I’m the first to mention this one.

Usually I only watch the first couple of seasons of a new show, then I lose interest (for example, I stopped watching Friends after they got rid of the monkey).

Cheers
Seinfeld
The Simpsons
MST3K
The Brady Bunch
Gilligan’s Island

Well, also I saw every episode of The Mike O’Malley Show, all both of them.

Every Episode –
Oz
LA Law
Dallas
Dynasty
Mary Tyler Moore
The Big Valley
The Hogan Family
I Love Lucy