Lost was very awesome and had a big impact on my life at the time. Other great series that spring to mind are Neon genesis Evangelion, Breaking bad, Dexter, 24 for pure escapism and adrenalin, sons or anarchy is cool as well, and you can't beat good old Dr Who
Mad Men and Breaking Bad are great television shows. Best overall would include the above two and The Wire, The Sopranos, The Shield and Battlestar Galactica.
Huge fan of The Big Bang Theory and Two and a half men. Sadly, Charlie Sheen acting out of his mind might mean the end of the latter. And among concluded shows, Seinfeld and Friends would clinch top spots. Like a lot of animes too, but best to save that for another discussion.