"Iconic" is word I've come to discover gets thrown around very liberally. People will seriously confuse it with "trendy", or worse, "What I really like in particular." For instance,
this list here. Lafayette is certainly an interesting character, but he has no value to anyone who has not seen an episode of True Blood. Iconic is something that has value independent of its being consumed. It's one of those things were a diletentte is equally suited to compiling a list as a maven. (Though perhaps not always. My dad could name more characters from McHale's Navy than Star Wars)
Coming up with iconic characters is often difficult for television, especially lately. This is largely because someone has to have some kind of idiosyncratic, or at least singular look. (Like the Bride from Kill Bill's yellow outfit.) With TV, there's a sense that doing that can lead towards kitsch. If I were to list the most iconic TV characters this latter half of the decade, they would probably have strange (Or at least alliterative) names, or maybe some kind uniform. Your Sue Sylvesters,your Don Drapers, your Claire Bennetts, your Sylars. I'm pretty sure no gym teacher will ever be able to don a track suit without realizing the implications. But in a lot of ways, pop culture has not only become less idiosyncratic, but less formal. (I wonder if it's one of the contributing factors to backlash over Twilight or Judd Apatow movies. It's the same resentment one gets when you see one of the younger guests to the wedding wearing what found in his hamper) I think it's also one of the reasons TV has become so insular, show-to-show. All those icons and gifs for TV shows feel more like in-jokes than cultural shorthand. In fact, I think Lost is practically anti-iconic; In the future it will be renown as uniquely unsuited to distillation. (Although, if you do simplify your concept and give it a distinctive look, for your troubles Seltzer and Friedberg will dress an actor up like them and do a moronic pratfall.)
I've also been thinking about properties that are iconic but can lack a singular representative--when the concept as a whole has caught on, but not on singular figure. Like, let me put it this way. Some characters manage to be iconic, even when everything else about their mythology is not well know with the public. (The Hulk, Buffy). Some are very rich, with maybe a famous singular character, but antagonists and supporting characters have taken an even bigger life of their own. (Star Wars, The Wizard of Oz) But sometimes, the general idea of something with be well known to everyone, as opposed to a figure. For instance, Planet of the Apes, Ninja Turtles, or Little Women. Sure, the fans will know that the turtles are name after Renaissance artists, and that one of the sisters is not, in fact, named "Laurie". It's what I've call "generic iconic". Where some kind of number (usually four), and some kind of look (girls in bonnets, turtles in bandannas) have some kind of cachet, even in the name value is not there.