Top 10, eh? I'm not sure I've even watch the the full series of 10 quality shows, and I'd find it a little weird to include shows I haven't watched every episode of, and I don't feel shows like The OC, One Tree Hill and Criminal Minds really qualify for inclusion ;-)
Let's give it a whirl though:
1. The Wire
2. South Park
3. The Sopranos
4. Breaking Bad
5. Arrested Development
6. The Office (UK)
7. The Office (US)
8. Dexter
9. House
10. Seinfeld
There's a distinct possibility that Breaking Bad can overtake The Wire and South Park after the final season, but as of yet those two are the pinnacles of their respective genres.
Shows like Prison Break and Lost were omitted because the couldn't keep my attention as they progressed, but if Prison Break had ended after the first season it would have been top 5 easily. Heroes would probably have been in there as well if they had kept it up after the first season, as I'm a sucker for anything that involves superpowers! But it just got progressively worse after that.
Game of Thrones and Boardwalk Empire are also shoo-ins at making the list eventually, but I feel it's too early to judge them after just one season, given how those two above turned out.