The Wire is probably the best show I've seen but my favourites along with The Wire are The Soprano's, Band of Brothers, Breaking Bad, Sons of Anarchy, Dexter and Game of Thrones (Have really high hopes for it to be HBO's next best thing), Deadwood, Carnivale, Six Feet Under.
Depends really on what genre for drama I'd say the above lot, Sci-fi wise I'd say Battlestar Galactica(up there with The Wire in terms of quality), Doctor Who, Farscape.
Comedy is hard as I love so many:- Arrested Development, It's Always Sunny in Philadelphia, The Office UK and most of the US ones, Spaced, Only Fools and Horses, Blackadder, Red Dwarf, Community, Curb Your Enthusiasm, Fawlty Towers, Peep Show.
Animated:- South Park, Futurama, Archer.
Honerable mentions:- 24, The Shield, Mad Men, The League of Gentlemen, I'm Alan Partridge, early Family Guy before it turned into utter garbage (Seasons 1-5 or so), 50% or so of The Simpsons.
I've probably seen most shows out there from the past 25 years or so and all of the above would be my recommendations, probably missed a few shows that I'd recommend too, I'll edit back later if I can think of any.