You people have a lot more free time than I do.
As for me
ST:TOS
The Prisoner
Police Squad
I’ve seen most of some other series more than once, but without the DVD set I couldn’t be sure. Most of ST:TNG but not all.
Going out on a limb - maybe they bought the DVD set? Or watch it on HBOGo (I assume it’s available there).
The SandBaggers
Homicide: Life on the Street
Rome
Firefly
Babylon 5
Star Trek: Deep Space 9
Twin Peaks
Wolf’s Rain
Escaflowne
Sherlock Holmes (Jeremy Brett starring)
Farscape
Oh, and Dr Who (last three doctors). I’ve also watched the first Red Dwarf season a few times. And someone mentioned HHGTTG, I consider that more of a miniseries but I’ve watched that a few times too. If we are counting miniseries, then I’ve watched The Lost Room at least five times if not more.
Mostly from TV repeats but all of the Treks I videoed off air and re-watched. Sky repeated NG, VOY and DS9 over and over.
ST:TOS
ST:NG
ST:VOY
ST:DS9
ST:ENT
Originally seen as a kid, and revisted at least once.
Stingray
Thunderbirds
Captain Scarlet
UFO
(You notice, of course, the omission of Joe 90, ugh)
Tom and Jerry (the Fred Quimby ones) this counts right?
Box sets UK:
Spaced - this gets re-watched frequently
The Hitch Hiker’s Guide to the Galaxy - although I re-visit the original radio version far more often.
The IT Crowd
Black Books
Jonathan Creek (may watch again in 10+ years once I’ve had time to forget the twists)
Sherlock
QI
I obviously have the entire Clangers set, but that’s probably not quite what the OP had in mind.
US:
The Rockford Files
Monk
Bones 1-5, I hear it started to SUCK BADLY after this
Psych (recorded off air I’ve got everything we’ve had over here so far)
House (recorded up to around series 6, got burned out a bit and I really don’t want to see the House/Cuddy ro-frackking-mance, if that indeed happened)
I have Police Squad but surely that’s too short to count?
Edit: Add The Big Bang Theory. But you probably guessed that.
Lordy, this makes it look like I do nothing but watch TV!
The Dick Van Dyke Show
Star Trek TOS
Babylon 5
Good Neighbors (The Good Life)
All Creatures Great and Small
Monty Python
The Prisoner
Fawlty Towers
Yes, Minister
Yes, Prime Minister
Rocky And Bullwinkle - Mooseberry bush, Upsidasium, Metal-munching Moon Mice
I, Claudius
Band of Brothers
Lonesome Dove. X2
The Wire (just finished my 5th time through all of it)
Twin Peaks (at least that many times)
Damages
Arrested Development
Dexter
Rome
The Office (UK version)
Luther
Firefly
Breaking Bad
Buffy the Vampire Slayer
Rome
Game of Thrones
Six days, and nobody’s bit?
OK, fine, it’s not too short, and don’t call me Shirley.
Off the top of my head, probably quite a few cartoons, either of the saturday morning or afternoon after-school variety when I was growing up (and a lot of the sitcoms previously mentioned, from the days before cable). A year or two ago, I noticed one of the cartoon networks was showing “Wacky Races” right around my bedtime, and I ended up watching until I realized I had seen them all again multiple times.
Blake’s 7 (would probably be viewed even more, if they’d ever release it on DVD in the US)
Doctor Who, Doctors 3-5 (I think twice for pretty much all of their runs)
Are You Being Served
Sledge Hammer!
The Muppet Show
Special Unit 2
The Original, True, Battlestar Galactica. Which means I saw the sequence of the Viper tracking blaster fire to track and destroy the Cylon ship about 20,000 times.
Coupling, the British version. I have seen it so many times and it always makes me laugh.