I’m not sure I recommend Heroes anymore - not because it’s not good (it’s very good), but because the writers’ strike appears poised to make it dead midway through this second season. That’s something I don’t think I’d want to get hooked on, if I weren’t already.
From the US:
Carnivale - died an untimely death, but was the single best television show ever.
Buffy the Vampire Slayer & Angel - depending on what exactly you liked about Firefly, you may well like those (persevere through the first season for each - they’re still okay, but had not hit their strides).
Twin Peaks - now out entirely in one DVD boxed set that I must have. First season’s awesome, but I haven’t seen the pilot or second season, as they’ve been very hard to come by up until now.
Jeremiah - often overlooked post-apocalyptic show about a world that was hit by a plague that killed everyone who’d gone through puberty (with, it turns out, a few exceptions). Loosely (and I do mean loosely) based on a French or possibly Belgian comic I’ve never read. Primary reason to watch: It’s J. Michael Straczynski’s non-Babylon 5 show. Unfortunately the second (and last) season doesn’t seem to be out on DVD nor on its way to DVD. You can stream it from Netflix’s Watch Now or hit up torrent sites, though.
American Gothic - interesting show about a creepy Southern sheriff and the town he runs. Episode quality varies fairly widely and it’s not a continuous plot the way most of these other shows are - kind of predates that era of television. Still, there’s a certain amount of timeline progression, which makes it very frustrating that the show was aired out of order and put on the DVDs in air date order - the DVD people even knew what the proper order was, and put it on their site, but not on the damned DVDs. :P
Ultraviolet - very well done series about a small covert government agency tasked with researching and countering the activities of vampires (though they never use the word, referring to them instead as “Code Fives” (V)).
The House of Cards Trilogy - political drama about a devious, manipulative, and ruthless member of Parliament’s maneuverings towards the Prime Minister’s role (and his subsequent efforts to stay in power). He’s a very charismatic character, but not at all a nice man.
The Sandbaggers - excellent 70s series about the Special Operations Directorate of the British foreign intelligence service (MI-6, I think. But I forget). Very realistic treatment - no James Bond gadgets and high action theatrics, but plenty of politicking and tense covert action. Three series in all, with the storyline ending a bit abruptly as unfortunately the show’s creator and primary mover disappeared mysteriously before he’d completed it.
The Prisoner - if you don’t know about this one…
Black Adder - the first series has the highest production values but is the least of the four in my opinion. Series two and three are hysterical and make excellent use of their historical background. Four is less funny overall but, well, it is set during the first World War, which means a certain somberness creeps into things. The last episode is positively tear-inducing. Oh - it is a Britcom, so if you don’t like that brand of humor…ah well.
The League of Gentlemen (not to be confused with the League of Extraordinary Gentlemen. Really really different.) - How to describe this show…hmm. It’s…uh…it’s kind of like Monty Python crossed with Twin Peaks or something similarly bizarre and somewhat unsettling. There’s the usual skits (more or less) and the inherent comedy of having a handful of middleaged men play most every character of either gender. But there’s a darker edge to it. The proprietors of the Local Shop dance naked around a bonfire and do strange and terrible things to non-local visitors. The butcher sells a secret “special” meat. The veterinarian tends to kill animals he treats in spectacular manner (not intentionally). The weird, creepy traveling carnival proprietor winds up fleeing the town screaming.