My vote is for Heroes. Great plot, lots of cliff hangers, well developed characters. DH and I started watching it a few weeks ago on Netflix and I must confess we have been up until midnight almost every night watching multiple episodes. Gotta stop this and get some sleep!
Our family has several favorites: Heroes, Fringe, Leverage, Chuck, House, Bones, but I am the only one addicted to Lost. We also love The Big Bang Theory--especially Chuck Lorre's vanity cards at the very end of the show.