The Wire. Everything everyone says about it is true.
Deadwood. Al Swearengen is one of the greatest fictional characters based on a real-life person ever. Cocksucker.
Alias. J.J. Abrams finds various reasons for Jennifer Garner to dress in underwear and swimsuits. With a kick-arse cast of character actors, and ridiculous macguffins, this is very enjoyable T.V.
The West Wing started in '99, and Buffy in '97 so I don't think they count, however I should say that Aaron Sorkin writes so well it makes me a little high.
There are plenty of TV shows I really like such as The Mighty Boosh, The IT Crowd, The Flight of the Conchords, but you can't compare them to the big guns.