At Comic Con this year, Tim Kring showed some part of Episode 1 of Season 3 of Heroes containing major spoilers. I am still waiting for a complete set of Youtube videos to appear of the whole Heroes coverage, I'll post it as soon as someone uploads it. Though if you want to be spoiled, read the summary of the preview shown: http://www.heroestelevision.com/heroes-season-3-episode-1-spoilers/
At Lost panel this year, Matthew Fox (Jack) made a surprise appearance with Damon and Carlton. They showed a Dharma Video of the familiar Dr Candle, in which he revealed his real name and explained Time Travel.
Watch the Lost coverage on youtube: