My so-called Life
Tenspeed and Brownshoe.
Young Indiana Jones, though actually, glancing at wiki, it apparently went on longer then I thought it did (three seasons, I seem to vaguely remembering thinking it ended after one, ah well, good show anyways).
As others have mentioned, I would’ve liked a third season of Rome. They were pretty obviously setting it up to move to the Holy Land during Octavians reign, which I would’ve liked to see.
I’ll second Brimstone and Earth2 as well.
Cupid and the 1998 version of Fantasy Island are the first that came to mind–even before Firefly, which I’m not listing because even without reading the thread I’m sure half a dozen people already have.
Also The Days & Nights of Molly Dodd. (I’m such a girl sometimes.0
I was just reminded of how much I loved Boomtown when a friend got the DVDs. I can’t figure out how that show never found its audience.
Freaks and Geeks
NewsRadio
WKRP
Bob
MST3K
Dinosaurs
Probably a bunch of others, but those are on the top of the list.
*Shannon’s Deal * - John Sayles penned lawyer show where the lawyer never sees a courtroom. Still own the pilot telemovie on VHS.
American Gothic - Got completely screwed by the networks, (Characters removed, episodes shown out of order.). Still getting screwed on DVD (Episodes still out of order, significant amount of discs faulty). But it did have one of the greatest series ending episodes ever, which we thankfully got to see in Australia.
Deadwood & Firefly obviously.
Another vote for Brimstone.
Despite it’s many flaws, Studio 60 needed more time to find the funny. At the very least they could have given the better characters a spinoff.
Gargoyles, I think. I always caught them out of order, so I wasn’t able to follow the story lines…
I’m currently watching Freaks and Geeks on DVD, because people here have mentioned it. Cute little show. I enjoy it, but don’t see how much longer it could have gone on.
The youngest ones who are supposed to be what, 9th graders? They look and act like 5th graders to me.
I get a sharp pain in my heart every time someone mentions Brimstone.
Keen Eddie and Due South, as well.
For me, while I agree with many of the other worthy shows mentioned in this thread (especially WKRP in Cincinnati and Freaks and Geeks ), I gotta go with Strike Force .
Robert Stack, as always, was awesome, and in addition to the hyper-violence (as mentioned in the Wiki article, “at one point the series was labeled the most violent in American TV history”) there was a veritable motherlode of black comedy and some very un-PC moments.
There will never be another… 
I know it’s silly, but Jack & Jill.
Two from last season – Raines with Jeff Goldblum and Kidnapped with Jeremy Sisto.
Ditto Deadwood, Rome, Carnivale, and I also liked the one with Phoebe from Friends – The Comeback.
I’m betting “Friday Night Lights” doesn’t get renewed for a third season, which would be a real shame because it’s the best show on network TV.
Secong “Studio 60…”
“The West Wing” could have gone on forever as far as I’m concerned, although it wasn’t short lived. The last season was one of its best.
Stark Raving Mad—
A nice, quirky little comedy with Tony Shaloub as a somewhat deranged horror writer. Also featured Neal Patrick Harris as Niles Crane.
Cybersix—
Saturday morning cartoon, based off of a semi-underground Argentinian B&W comic about an escaped Nazi bioroid who disguised herself as a hooker to fight monsters, and who "drag-king"ed her secret identity. ::Sniff:: That show really had heart. Nice theme song, too.
I don’t unerstand what you mean. WW ended with that horrible unresolved cliffhanger–Zoey Bartlett being kidnapped–because Aaron Sorkin got booted out and the entire cast and crew simultaneously and independently said, “Screw financial security. I’m in this for the art, and without Sorkin this series will suck.” It was very sad.
I can’t tell if you’re being tongue-in-cheek here, but there were a couple of lesser seasons after that one, and the final season was back to the Sorkin levels.
:: checks your post count ::
No, you’re not new. We just haven’t crossed paths afore now. Hmm.
Anyway…
Heretic! Light the torches, men, we’re storming Mundane’s castle! 
Keen Eddie was definitely killed off before its time. Lovely show. Very funny. Have to agree with you about Freaks and Geeks. That seemed like a good stopping place. Maybe one more season would have worked.
For myself, I really liked The Dresden Files. I know fans of the books (which I am now reading) felt that the show was a bit of a travesty, but taken for what it was, it was a lot of fun, and I’d like more of it.
Eyes
Rome
Firefly
Whatever Joss does next on TV that is killed way too early.
I will mention a show probably no one has ever heard of or seen, but I absolutely loved:
“Nowhere Man”. It ran back in 1995 and starred Bruce Greenwood as a photographer whose entire life is erased by “them”. He has a big opening at a gallery and afterwards he and his wife go out to eat. He goes to the bathroom and when he comes back, some other couple is sitting in his seat. His wife is gone. And his entire life unravels from there. No one knows him. No one remembers him. It is as if he never existed. Imagine “The Net” taken to unbelievable extremes.
The show only ran for one season, and just when the audience is beginning to see how this happened and who might be responsible, it was cancelled. Very disappointing. It was a very ambitious show for (at the time) a brand new network.