Modern Day Holy Grail?

I was perusing Parade Magazine this afternoon, and came across this picture in an article:

Ahh yes, good old Honus Wagner's T-206.  Even non-collectors know this card, and many know the story behind it.  The magazine noted that this card is "considered to be the holy grail to many collectors."

That's all well and good, and this Wagner card is certainly one of the most recognized before (I would argue at least) the 1952 Micky Mantle.  But the statement got me thinking about something.

Taking the Wagner card and the '52 Mantle card out of the mix, what are some other cards that collectors consider "holy grails?"  I know this is different for each collector, in terms of their own personal collections (for example, I'd consider certain Halladay cards holy grails for me), but collectively, within our community in this modern day, what cards are revered most?

I can pick out a few, but I'm honestly stumped on a long list:  2010 Topps Stephen Strasburg rookie, 2011 Bryce Harper rookie(s), but which ones?

Just a thought I am pondering on this rainy Easter Sunday.  Feel free to chime in if you have any thoughts of your own on modern day holy grails.