And what’s the most number of times you’ve watched a series?
ST: DS9, 4 times over a handfull of years.
ST: Enterprize 2 times
:o
Wonderfalls: 3 or 4 times
Pushing Daisies: 4 or 5 times, easy.
Off the top of my head:
I love Lucy
The Honeymooners
The Odd Couple
Taxi
The Brady Bunch
Seinfeld
Curb Your Enthusiasm
Laverne & Shirley
WKRP in Cincinnati
The Twilight Zone (original)
You missed Happy Days?
I’ve seen every episode of Kim Possible. and the movies.
Firefly
West Wing
Star Trek: original series, Enterprise, and I think I got all of Next Generation.
MASH
I Claudius
The Civil War
Monty Python’s Flying Circus
Star Trek
Fawlty Towers
Arrested Development
The Prisoner
The Wire
Deadwood
Buffy
Angel
Firefly
And after this week is over, The Sopranos. “Kennedy and Heidi” was on last night. Just two more episodes to go.
ETA: Poldark and The Forsyte Saga
I’m quite sure I’ve seen every episode of certain syndicated shows multiple times (Dick Van Dyke, MASH, Bonanza, Bewitched, I Dream of Jeannie, Gilligan’s Island, ST:TOS, ST:TNG, etc.) The series I own and rewatch all the time are:
BtVS
Angel
The Avengers (Emma Peel years)
WKRP (bootlegs with original music)
Babylon 5
Fawlty Towers
Good Neighbors
Rocky & Bullwinkle & Friends
Animaniacs
Firefly
Thin Blue Line
Jack of All Trades
Wings
The New Avengers
Father Ted
Connections
Connections 2
Connections 3
The Day the Universe Changed
I considered it, but I’m not certain if I saw the last season or two more than once. Same with MASH.
I’ve seen every episode of Pushing Daisies three times (though, with only 22 episodes, it’s not tremendously difficult).
Same thing for Firefly; with only 14 episodes, I know I’ve seen every episode twice (intentional runs through my DVD set), but I’m pretty certain that I’ve seen every episode at least one additional time through showings on Science Channel.
I’m reasonably certain that I’ve seen every episode of the original Star Trek, and WKRP in Cincinnati, multiple times, but as those were picked up through many years of re-runs, I can’t give a good number for those. 
Firefly - at least 10 times
Sopranos - 4 or 5 times
Deadwood - 4 or 5 times
The Monkees - 4 or 5 times
Friends - probably about 100 times
I think I watched Fullmetal Alchemist twice, the first time on TV (probably slightly out of order), and once straight through.
I think I also watched Fooly Cooly 3-4 times because it’s only 6 episodes.
Granted, the number of TV series I’ve watched total is not much bigger than that list, so the number I’ve seen more than once is bound to be small. (New) Doctor Who and Torchwood are the only other series I can think of that I’ve seen all the way through off the top of my head. I have a tendency to get bored halfway through TV series and do something else.
I’m not going to count Brady Bunch, Happy Days, Partridge Family, etc. which I watched only because that was pretty much all that was on at the time, and not because I actually enjoyed those shows.
ST:TNG probably twice
ST: TOS an untold number of times
Babylon 5 twice
X-Files probably 3 times
Firefly 4 times
Arrested Development 5 times (season 4 twice)
Firefly x3
Babylon 5 x3
Deadwood x2
Fawlty Towers x4
Drop the Dead Donkey x2
Futurama (S1-S4 lost count)
Band of Brothers x2
Ultraviolet (UK vampire series) x2
I have the DVD’s of these and have watched each several times (UK series in italics.)
(Aaron Sorkin)
West Wing
Sports Night
Studio 60
(Crime)
CSI (Vegas)
Law and Order (+ Law and Order Criminal Intent)
Life
Nero Wolfe Mysteries
Sherlock
Jonathan Creek
(Spy)
Tinker, Tailor, Soldier, Spy
Smiley’s People
(Comedy)
Big Bang Theory
Two and a Half Men
Entourage
Yes Minister (+ Yes, Prime Minister)
Porterhouse Blue
There are a number of series where I’m sure I’ve seen all of the episodes at least twice due to reruns, but I’m assuming you’re talking about watching them all in order from some canned source such as Netflicks, On Demand, or DVDs.
Twin Peaks I’ve seen at least 3, maybe 4, times and I’m sure I’ll watch it again at some point, since I have the DVDs. Fawlty Towers I’ve seen at least 3 times. I’ve see all of Monty Python’s Flying Circus at least twice.
I’m not sure if Breaking Bad counts, since it still has a handful of new episodes starting in August, but I’ve seen all of it to date at least twice.
ST:TOS (infinity number of times)
ST:TNG (infinity minus 1)
Firefly
Keen Eddie
Life On Mars (UK)
HHGTtG (80s version)
Profit
The various Star Treks
Buffy, Angel, Firefly
How I Met Your Mother
Quantum Leap
Futurama
Not sure how many times, probably at least three. The Whedon shows I actually deliberately watched alone and with friends on DVD several times. The others I caught daily in syndication.
I watched each new Lost several times, partly because I liked it and partly because I worked on the wiki. I plan on doing a complete rewatch when the Bluray comes down in price.
I also tend to watch new episodes of Dexter, True Blood, New Girl, Big Bang Theory, and Glee once on my own and once with a friend, as well as some of the SyFy shows.
**Star Trek
The Prisoner
Connections
The Day the Universe Changed
The Outer Limits
**
Probably The Twilight Zone
Freaks and Geeks
Tremé