#1 - #3 - Buffy the Vampire Slayer, Angel and Firefly
#4 - Futurama
#5 - Cracker (British version)
#6 - Nova
#7 - The Shield
#8 - Carnivale
#9 - The Sopranos
#10 - Deadwood
Honorable Mention: Millenium, Batman: the Animated Series, X-Files, The Simpsons, Monty Python's Flying Circus
Starting at the top, "Buffy the Vampire Slayer" sounds like it should be catastrophically lame. I thought so every time I heard about it. Until I watched an episode. Turns out, it's well-written as a drama and as a comedy, really like nothing else there is.
Angel was a spin-off of Buffy. Less with the coming-of-age, more with the action, but still great entertainment.
Firefly was cancelled far, far too soon, but it works very well, with some great and memorable characters and, again, a concept that's a little bit outside typical science fiction.
All three shows were created by Joss Whedon. All three have well-written dialogue and true-to-life characters who develop over single episodes and multiple seasons. Which one I like best at any particular time depends on which one I've seen most recently.
Futurama managed to be funny, smart and irreverent throughout its run - sorta like the best years of "the Simpsons". I loved how the writers would throw in random, working science (e.g. see the equations on that piece of paper? They work out.) in the middle of whatever was going on. Futurama always made me laugh. Lesser animated comedy programs cannot do that.
Cracker is something I found on DVD. It stars Robbie Coltrane, who in the USA is probably best known as Haggrid in the Harry Potter movies. But in Cracker, he's a degenerate gambler, an unrepentant drunk and a slovenly fat guy. And a first rate psychologist who, bored with his teaching job and in need of extra cash, takes up criminal investigation. Robbie Coltrane is the complete opposite of a Hollywood leading man, and for me that's big part of the charm.
Nova is a science documentary program, the first one I can remember seeing. It's always very interesting and enjoyable, and is a compelling argument in favor of public broadcasting in the USA.
The Shield is an intense police drama. In the US it's shown on a cable channel, and therefore shown with less censorship than it might otherwise have. Again, there's strength in both writing and characterization, which is not surprising given that the series creator used to work for Joss Whedon.
Carnivale is very difficult to properly describe. It's a period drama, set in the dust-bowl western USA of the 1930s. Its pacing might be called slow or almost glacial, but there's a heightened sense of mystery and weirdness that shows like the X-files were never able to maintain. It also has some of the coolest scoring I've ever heard on a TV show. Carnivale was cancelled after only two seasons, and the ending was sadly rushed. I hope it'll be back in a different form someday.
The Sopranos. What's not to love? It's a family drama. It's a crime story. It's an ongoing tragedy. Sometimes there are naked women (yay!). "The Godfather" might be every mobster's fantasy, but the Sopranos is apparently so close to reality that a couple of real-life New Jersey gangster types were caught discussing whether or not the Sopranos were based on THEM.
Finally, Deadwood. I didn't really see myself enjoying a western. This is a show that's all about the taciturn walking contradiction that is Sheriff Bullock, and Al Swearingen, with a shakespearean command of the foul-mouthed soliloquy, he may very well represent the best-written character on any television show currently being broadcast.
It shouldn't be too surprising that all of the last three shows are HBO products. HBO, it seems, makes its business by not shoveling the same shit as US broadcast TV networks.