According to HBO this is the Iron Throne...
And this is how GRRM envisioned it while writing.
In a recent LiveJournal post, Martin expressed that artist Marc Simonetti has gotten the closest to the Iron Throne he sees in his head. Though admitting it would be an impractical iconic set piece for television:
This Iron Throne is massive. Ugly. Assymetric. It's a throne made by blacksmiths hammering together half-melted, broken, twisted swords, wrenched from the hands of dead men or yielded up by defeated foes... a symbol of conquest... it has the steps I describe, and the height. From on top, the king dominates the throne room. And there are thousands of swords in it, not just a few. This Iron Throne is scary. And not at all a comfortable seat, just as Aegon intended.