Alien Nation
Babylon 5
Battlestar Galactica (2003)
Boston Legal
Californication
Curb Your Enthusiasm
Dexter
Farscape
Futurama
Millennium
The Prisoner
Red Dwarf
Six Feet Under
Star Trek (1969)
Star Trek: Deep Space Nine
Twenty-Four
The Twilight Zone (1959)
The West Wing
The Wire
The X-Files
Babylon 5
Battlestar Galactica (2003)
Boston Legal
Californication
Curb Your Enthusiasm
Dexter
Farscape
Futurama
Millennium
The Prisoner
Red Dwarf
Six Feet Under
Star Trek (1969)
Star Trek: Deep Space Nine
Twenty-Four
The Twilight Zone (1959)
The West Wing
The Wire
The X-Files


Also, I'm not counting any series where I've seen fewer than 20 or so episodes, because there needs to be some minimum limit to get a good sense of whether they can maintain quality long term. Dexter is an exception because I fully expect S2 to keep it at least in the #3 slot - #3 with a power drill
- when I finally get those DVDs in a couple weeks. Since I ran out of shows worth listing, I gave the last two slots to two shows that I fully expect to make the list legitimately by the end of next season.