The ones that most qualify for me are:

* Minecraft: This will probably hold the position Pac Man holds to us. Single biggest culture-marker perhaps.

* Taylor Swift: She's like Michael Jackson was (perhaps because of access and audience size improvements)

I don't know if Wikipedia or the mainline social media websites would count. People remember The Myspace Era. Tumblr and Twitter have reputations for their culture but would they be classics? Hard to tell.