As a giant TV nerd, here's what I genuinely think are the best of the decade (only 2 HBO shows!); they might not be terribly original choices, but there were only so many truly great shows:

The Wire
Arrested Development
Deadwood
Battlestar Galactica
Buffy the Vampire Slayer
Lost
Mad Men
Life on Mars (UK)
Veronica Mars
30 Rock
The Office (UK)
Friday Night Lights
Daria
Dexter
Everwood

And, though perhaps not the best, 4 of my favorites are:
Spaced
Black Books
The Middleman
Doctor Who